Value returns ndarray for dataframes with a single column with datetime64 tz-aware
 - [x] closes #14052
 - [x] tests added / passed
 - [x] passes ``git diff upstream/master | flake8 --diff``
 - [x] whatsnew entry

# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15736?src=pr&el=h1) Report
> Merging [#15736](https://codecov.io/gh/pandas-dev/pandas/pull/15736?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27?src=pr&el=desc) will **decrease** coverage by `0.02%`.
> The diff coverage is `86.48%`.


```diff
@@            Coverage Diff             @@
##           master   #15736      +/-   ##
==========================================
- Coverage   91.01%   90.99%   -0.03%     
==========================================
  Files         143      143              
  Lines       49380    49402      +22     
==========================================
+ Hits        44944    44953       +9     
- Misses       4436     4449      +13
```


| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/15736?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/core/generic.py](https://codecov.io/gh/pandas-dev/pandas/compare/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27...6cd4832c31190dce17e62221fd02225279acc44b?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ2VuZXJpYy5weQ==) | `96.24% <100%> (ø)` | :arrow_up: |
| [pandas/core/internals.py](https://codecov.io/gh/pandas-dev/pandas/compare/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27...6cd4832c31190dce17e62221fd02225279acc44b?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvaW50ZXJuYWxzLnB5) | `93.49% <85.71%> (-0.1%)` | :arrow_down: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/compare/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27...6cd4832c31190dce17e62221fd02225279acc44b?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `25% <0%> (-58.34%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/compare/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27...6cd4832c31190dce17e62221fd02225279acc44b?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.86% <0%> (-0.1%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/15736?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/15736?src=pr&el=footer). Last update [9ab57dc...538af78](https://codecov.io/gh/pandas-dev/pandas/compare/9ab57dc522a41d42cb230272a3a0df0ad8a7eb27...538af7833120f2a1df09af8a61ec8eb75370e21a?el=footer&src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments). @sdementen I merged #15765 so I think this will be quite a lot simpler now. @sdementen rebase / update? can you rebase and update? @jreback I am currently overloaded, I'll have to wait for a better period with some free time ! good ideas, needs a rebase / update. pls comment if you'd like to continue.