CLN: removed unused "convert" parameter to _take
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

Followup to #20841: the ``convert`` parameter to ``_take`` is irrelevant: the conversion of negative to positive indices is required only for ``Categorical``s (and only until we normalize their ``take`` behavior with negative indices).
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20934?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@2ab3727`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `84%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/20934/graphs/tree.svg?token=eZ4WkYLtcO&src=pr&width=650&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/20934?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #20934   +/-   ##
=========================================
  Coverage          ?   91.81%           
=========================================
  Files             ?      153           
  Lines             ?    49474           
  Branches          ?        0           
=========================================
  Hits              ?    45424           
  Misses            ?     4050           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.21% <84%> (?)` | |
| #single | `41.85% <36%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/20934?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/groupby/groupby.py](https://codecov.io/gh/pandas-dev/pandas/pull/20934/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9ncm91cGJ5LnB5) | `92.58% <100%> (ø)` | |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/pull/20934/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.02% <100%> (ø)` | |
| [pandas/core/indexing.py](https://codecov.io/gh/pandas-dev/pandas/pull/20934/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW5kZXhpbmcucHk=) | `93.55% <71.42%> (ø)` | |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/20934/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.13% <75%> (ø)` | |
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/pull/20934/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `95.93% <87.5%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/20934?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/20934?src=pr&el=footer). Last update [2ab3727...7aa63c2](https://codecov.io/gh/pandas-dev/pandas/pull/20934?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!

FYI a more complete linter command is:
       
`` git diff master --name-only -- "*.py" | grep "pandas" | xargs flake8``

(which catches unused things as well)
