CLN: Remove pd.parser, lib, and tslib
Title is self-explanatory.

xref #15537.
Hello @gfyoung! Thanks for submitting the PR.

 - There are no PEP8 issues in the file [`pandas/__init__.py`](https://github.com/gfyoung/pandas/blob/0f29c13c336a9196fa630ad430528eb4eb7f6b66/pandas/__init__.py) !

 - There are no PEP8 issues in the file [`pandas/tests/api/test_api.py`](https://github.com/gfyoung/pandas/blob/0f29c13c336a9196fa630ad430528eb4eb7f6b66/pandas/tests/api/test_api.py) !

 - There are no PEP8 issues in the file [`pandas/tests/api/test_types.py`](https://github.com/gfyoung/pandas/blob/0f29c13c336a9196fa630ad430528eb4eb7f6b66/pandas/tests/api/test_types.py) !

 - There are no PEP8 issues in the file [`pandas/tests/test_errors.py`](https://github.com/gfyoung/pandas/blob/0f29c13c336a9196fa630ad430528eb4eb7f6b66/pandas/tests/test_errors.py) !

 https://travis-ci.org/pandas-dev/pandas/jobs/447030560#L2519

`xarray=0.8.0` depends on `pandas.tslib` existing, hence the downstream failure (FYI, `xarray` is at `0.10.x` now, so this is pretty old).

@TomAugspurger : Do you remember why it was pinned in #20767?

Alternatively, because it's a Python 2.x failure, add a skip and move on? 🤷‍♂️  u can bump the xarray test > u can bump the xarray test

@jreback : To clarify, you mean bump the version number for the `xarray` dependency? it’s just the test version
we don’t depend on xarray  @jreback : Sorry, poor choice of words.  I meant to say:

We should just then bump the `xarray` version for that Travis build (e.g. `0.9.6`, when this is fixed). # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23378?src=pr&el=h1) Report
> Merging [#23378](https://codecov.io/gh/pandas-dev/pandas/pull/23378?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/051f4a2cf70f25649bae680d290cbf3ed77363ab?src=pr&el=desc) will **decrease** coverage by `0.05%`.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/23378/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/23378?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #23378      +/-   ##
==========================================
- Coverage   92.22%   92.17%   -0.06%     
==========================================
  Files         169      166       -3     
  Lines       51261    51250      -11     
==========================================
- Hits        47277    47238      -39     
- Misses       3984     4012      +28
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.6% <ø> (-0.06%)` | :arrow_down: |
| #single | `42.21% <ø> (-0.03%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/23378?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/\_depr\_module.py](https://codecov.io/gh/pandas-dev/pandas/pull/23378/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlcHJfbW9kdWxlLnB5) | `0% <0%> (-65.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/23378?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/23378?src=pr&el=footer). Last update [051f4a2...86e439e](https://codecov.io/gh/pandas-dev/pandas/pull/23378?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 nice, thanks!