CLN: remove tseries.util.pivot_annual/isleapyear
``pivot_annual`` and ``isleapyear`` in ``tseries.util`` were deprecated in v0.19.

This PR removes them from the code base.
Hello @topper-123! Thanks for updating the PR.



Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on November 21, 2017 at 21:05 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=h1) Report
> Merging [#18370](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b00e62c273cd60739b538314156b65f0f79350f9?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18370/graphs/tree.svg?width=650&height=150&src=pr&token=eZ4WkYLtcO)](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18370      +/-   ##
==========================================
- Coverage   91.38%   91.36%   -0.03%     
==========================================
  Files         164      163       -1     
  Lines       49790    49753      -37     
==========================================
- Hits        45501    45455      -46     
- Misses       4289     4298       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.16% <ø> (-0.01%)` | :arrow_down: |
| #single | `39.57% <ø> (-0.02%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |
| [pandas/tseries/offsets.py](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvb2Zmc2V0cy5weQ==) | `96.92% <0%> (+0.01%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=footer). Last update [b00e62c...38ed067](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=h1) Report
> Merging [#18370](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/c4a2cd362afdfbc21cb62a8e09758226e86735c4?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/18370/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #18370      +/-   ##
==========================================
- Coverage   91.36%   91.34%   -0.03%     
==========================================
  Files         164      163       -1     
  Lines       49733    49690      -43     
==========================================
- Hits        45439    45387      -52     
- Misses       4294     4303       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `89.13% <ø> (-0.01%)` | :arrow_down: |
| #single | `39.64% <ø> (-0.05%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.8% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=footer). Last update [c4a2cd3...151c40c](https://codecov.io/gh/pandas-dev/pandas/pull/18370?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 I've moved ``test_daily`` and ``test_monthly`` to ``testPivotTable`` from ``TestPivotAnnual``. ``test_hourly`` could be moved as well, but I'll do that tomorrow. thanks @topper-123  @topper-123 ok for a followup to move tests if you want.