[BLD] [CLN] Close assorted issues - bare exceptions, unused func
<s>- Removing numpy cimport from cython modules where feasible fixes the npy_deprecated1.7 ... warning.</s> <b>update</b> Nope!
- Catch specific exceptions in a handful of places.
- Removes unused function #19676
- Implement command-line option to enable cython coverage #21991

closes #19676
closes #21991
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

hmm still quite a few warnings (I am guessing that this AND the other PR will make progress on more of these?)

ideally we could run the --with-cython-coverage on a build at some point. though would have to find a way to display this. # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=h1) Report
> Merging [#22030](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/a6c7387cd43ddc45ac1a4a354c7ac5019fa69678?src=pr&el=desc) will **increase** coverage by `0.02%`.
> The diff coverage is `33.33%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/22030/graphs/tree.svg?src=pr&token=eZ4WkYLtcO&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #22030      +/-   ##
==========================================
+ Coverage   92.02%   92.04%   +0.02%     
==========================================
  Files         170      170              
  Lines       50707    50687      -20     
==========================================
- Hits        46661    46654       -7     
+ Misses       4046     4033      -13
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.45% <33.33%> (+0.02%)` | :arrow_up: |
| #single | `42.31% <33.33%> (ø)` | :arrow_up: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/util/\_decorators.py](https://codecov.io/gh/pandas-dev/pandas/pull/22030/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX2RlY29yYXRvcnMucHk=) | `91.34% <ø> (+9.08%)` | :arrow_up: |
| [pandas/io/s3.py](https://codecov.io/gh/pandas-dev/pandas/pull/22030/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3MzLnB5) | `86.36% <0%> (ø)` | :arrow_up: |
| [pandas/util/\_print\_versions.py](https://codecov.io/gh/pandas-dev/pandas/pull/22030/diff?src=pr&el=tree#diff-cGFuZGFzL3V0aWwvX3ByaW50X3ZlcnNpb25zLnB5) | `15.71% <0%> (ø)` | :arrow_up: |
| [pandas/core/tools/timedeltas.py](https://codecov.io/gh/pandas-dev/pandas/pull/22030/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvdG9vbHMvdGltZWRlbHRhcy5weQ==) | `98.41% <100%> (ø)` | :arrow_up: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=continue).
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> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=footer). Last update [a6c7387...65aad05](https://codecov.io/gh/pandas-dev/pandas/pull/22030?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 lgtm. can you rebase again, just want to see what kinds of warnings on build travis has now (this is the last in the series to remove warnings?) Will rebase in a bit, ok.  But note that the build-related parts of the PR were reverted they broke on windows. thank @jbrockmendel  @jbrockmendel build warnings are almost gone now! thanks!