DOC: fixups
* Fixed heading on whatnew
* Remove empty scalars.rst

If you look at http://pandas-docs.github.io/pandas-docs-travis/whatsnew/v0.24.0.html, you'll see that the TOC-tree is messed up. It includes every "level-3" header, since the highlights aren't nested under a "level-2" header.
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=h1) Report
> Merging [#24888](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6a745d826d9d5f5f46e208b0dad4d4ce0524defe?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24888/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24888   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        48425    48425           
  Misses       3988     3988
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `42.89% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24888?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/24888?src=pr&el=footer). Last update [6a745d8...a42e3b7](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=h1) Report
> Merging [#24888](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/6a745d826d9d5f5f46e208b0dad4d4ce0524defe?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24888/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24888   +/-   ##
=======================================
  Coverage   92.39%   92.39%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        48425    48425           
  Misses       3988     3988
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.81% <ø> (ø)` | :arrow_up: |
| #single | `42.89% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24888?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/24888?src=pr&el=footer). Last update [6a745d8...a42e3b7](https://codecov.io/gh/pandas-dev/pandas/pull/24888?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
