CLN: tslibs imports and unused variables
- [x] tests added / passed


- Remove unused imports, mostly `Py_ssize_t`, and variables
- Remove a block that is not hit after the `DatetimeIndex.normalize` performance upgrades https://github.com/pandas-dev/pandas/pull/23634 

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=h1) Report
> Merging [#24401](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3e0358d869f8a76b3223e8bb313a92edbaa369db?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24401/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24401   +/-   ##
=======================================
  Coverage    92.3%    92.3%           
=======================================
  Files         162      162           
  Lines       51875    51875           
=======================================
  Hits        47883    47883           
  Misses       3992     3992
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.71% <ø> (ø)` | :arrow_up: |
| #single | `42.99% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24401?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/24401?src=pr&el=footer). Last update [3e0358d...03f8c03](https://codecov.io/gh/pandas-dev/pandas/pull/24401?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/24401?src=pr&el=h1) Report
> Merging [#24401](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/3e0358d869f8a76b3223e8bb313a92edbaa369db?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24401/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24401   +/-   ##
=======================================
  Coverage    92.3%    92.3%           
=======================================
  Files         162      162           
  Lines       51875    51875           
=======================================
  Hits        47883    47883           
  Misses       3992     3992
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.71% <ø> (ø)` | :arrow_up: |
| #single | `42.99% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24401?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/24401?src=pr&el=footer). Last update [3e0358d...03f8c03](https://codecov.io/gh/pandas-dev/pandas/pull/24401?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!