MAINT: Drop take_last kwarg from method signatures
Affected methods:

1) `nlargest`
2) `nsmallest`
3) `duplicated`
4) `drop_duplicates`

xref #10236, #10792, #10920.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15710?src=pr&el=h1) Report
> Merging [#15710](https://codecov.io/gh/pandas-dev/pandas/pull/15710?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/5e96fb050afc192d464904f8f4a2a6e07723ee37?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `100%`.


```diff
@@            Coverage Diff             @@
##           master   #15710      +/-   ##
==========================================
- Coverage   91.02%      91%   -0.03%     
==========================================
  Files         143      143              
  Lines       49416    49396      -20     
==========================================
- Hits        44981    44951      -30     
- Misses       4435     4445      +10
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15710?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/indexes/base.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2luZGV4ZXMvYmFzZS5weQ==) | `96.14% <ø> (-0.01%)` | :x: |
| [pandas/core/base.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvYmFzZS5weQ==) | `95.48% <ø> (-0.03%)` | :x: |
| [pandas/indexes/multi.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2luZGV4ZXMvbXVsdGkucHk=) | `96.59% <ø> (-0.01%)` | :x: |
| [pandas/core/series.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvc2VyaWVzLnB5) | `94.89% <ø> (-0.02%)` | :x: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.87% <100%> (-0.11%)` | :x: |
| [pandas/indexes/category.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2luZGV4ZXMvY2F0ZWdvcnkucHk=) | `98.28% <100%> (-0.01%)` | :x: |
| [pandas/core/groupby.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS5weQ==) | `94.96% <100%> (-0.03%)` | :x: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :x: |
| [pandas/tools/merge.py](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=tree#diff-cGFuZGFzL3Rvb2xzL21lcmdlLnB5) | `93.68% <0%> (-0.34%)` | :x: |
| ... and [1 more](https://codecov.io/gh/pandas-dev/pandas/pull/15710?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15710?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/15710?src=pr&el=footer). Last update [5e96fb0...b416290](https://codecov.io/gh/pandas-dev/pandas/compare/5e96fb050afc192d464904f8f4a2a6e07723ee37...b416290aa310ae5af0a7dbd0066017c3583f8181?src=pr&el=footer&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). Separate issue: why did so many Travis builds get canceled (including my most recent one)? fixing travis so hold a bit to repush caching wasn't working for miniconda. turned it back on, then then found an error, fixed it, which led to the next one......soon. ok pull and try again. I *think* its fixed :> lgtm. ping on green. thanks!

keep em coming!