MAINT: Refactor Python engine empty line funcs
The Python engine's `_empty` and `_check_empty` methods were uninformative and undocumented.

This commit renames them to `_is_line_empty` and `_remove_empty_lines` respectively and provides appropriate documentation.

xref <a href="https://github.com/pandas-dev/pandas/pull/15925#discussion_r110377233">#15925 (comment)</a>



lgtm. ping on green. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=h1) Report
> Merging [#15946](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5d17a94506c9234abb6578e232a5bb4a921c851c?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/15946/graphs/tree.svg?height=150&width=650&token=eZ4WkYLtcO&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #15946   +/-   ##
=======================================
  Coverage   90.98%   90.98%           
=======================================
  Files         145      145           
  Lines       49556    49556           
=======================================
  Hits        45091    45091           
  Misses       4465     4465
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `88.75% <100%> (ø)` | :arrow_up: |
| #single | `40.57% <28.57%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/parsers.py](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhcnNlcnMucHk=) | `95.64% <100%> (ø)` | :arrow_up: |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `93.54% <0%> (-0.08%)` | :arrow_down: |
| [pandas/util/testing.py](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvdGVzdGluZy5weQ==) | `80.88% <0%> (+0.18%)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15946?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/15946?src=pr&el=footer). Last update [5d17a94...644d61b](https://codecov.io/gh/pandas-dev/pandas/pull/15946?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). @jreback : All green and ready to go. thanks!