Simplify to_pydatetime()
Up until #17331, `Timestamp.microsecond` was very slow.  So previously it was faster to go through `convert_to_tsobject` to get a new `datetime` instance than it was to just return 
 `datetime(self.year, self.month, self.day, self.hour, self.minute, self.second, self.microsecond, self.tzinfo)`

Now it is slightly faster (and much simpler) to do it this way.

Before:

```
In [2]: ts = pd.Timestamp.now()
In [3]: %timeit ts.to_pydatetime()
The slowest run took 13.88 times longer than the fastest. This could mean that an intermediate result is being cached.
1000000 loops, best of 3: 1.44 µs per loop
```

After:
```
In [2]: ts = pd.Timestamp.now()
In [3]: %timeit ts.to_pydatetime()
The slowest run took 8.51 times longer than the fastest. This could mean that an intermediate result is being cached.
1000000 loops, best of 3: 1.29 µs per loop
```

With a tz-aware Timestamp the speedup is much bigger:

Before:
```
In [4]: import pytz
In [5]: ts2 = ts.replace(tzinfo=pytz.timezone('US/Pacific'))
In [6]: %timeit ts2.to_pydatetime()
The slowest run took 39.71 times longer than the fastest. This could mean that an intermediate result is being cached.
10000 loops, best of 3: 68.9 µs per loop
```

After:
```
In [7]: import pytz
In [8]: ts2 = ts.replace(tzinfo=pytz.timezone('US/Pacific'))
In [9]: %timeit ts2.to_pydatetime()
The slowest run took 8.29 times longer than the fastest. This could mean that an intermediate result is being cached.
1000000 loops, best of 3: 1.47 µs per loop
```

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=h1) Report
> Merging [#17592](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/b3087efed7321bcfbfa86143bb81e93bc4552eda?src=pr&el=desc) will **decrease** coverage by `0.01%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/17592/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #17592      +/-   ##
==========================================
- Coverage   91.19%   91.18%   -0.02%     
==========================================
  Files         163      163              
  Lines       49627    49627              
==========================================
- Hits        45259    45250       -9     
- Misses       4368     4377       +9
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.96% <ø> (ø)` | :arrow_up: |
| #single | `40.19% <ø> (-0.07%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.77% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/17592?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/17592?src=pr&el=footer). Last update [b3087ef...235c8d0](https://codecov.io/gh/pandas-dev/pandas/pull/17592?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 LGTM, minus formatting nit. There is not, just added one. Hello @jbrockmendel! Thanks for updating the PR.



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

##### Comment last updated on September 21, 2017 at 22:48 Hours UTC Looks like someone added one overnight, will add to_pydatetime timing to it. Is there an error message in the circleci log that I'm missing? looks fine

you can click thru to circleci to see errors > looks fine
>
>you can click thru to circleci to see errors

I don't ask _just_ because I want to waste your time.  I'm saying I don't see any error message in the log.
 > I don't ask just because I want to waste your time. I'm saying I don't see any error message in the log.

I know, but some people don't actually realize you can click thru. yeah it prob timed out or something.

Wait till I merge #17619 and rebase thanks!