DOC: Improve the docstring of Timedelta.delta redux
- [ ] closes #xxxx
- [ ] tests added / passed
- [X] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

rather than trying to pick and choose items from my previous PR #21135 (which somehow had a number of other items sucked into it) ...
gonna start from scratch here and close out the old PR.

tried to incorporate changes noted in previous conversations with @WillAyd and @jreback (thanks for the guidance!)

```
################################################################################
###################### Docstring (pandas.Timedelta.delta) ######################
################################################################################

Return the timedelta in nanoseconds (ns), for internal compatibility.

Returns
-------
int
    Timedelta in nanoseconds.

Examples
--------
>>> td = pd.Timedelta('1 days 42 ns')
>>> td.delta
86400000000042

>>> td = pd.Timedelta('3 s')
>>> td.delta
3000000000

>>> td = pd.Timedelta('3 ms 5 us')
>>> td.delta
3005000

>>> td = pd.Timedelta(42, unit='ns')
>>> td.delta
42

################################################################################
################################## Validation ##################################
################################################################################
```
 
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21138?src=pr&el=h1) Report
> Merging [#21138](https://codecov.io/gh/pandas-dev/pandas/pull/21138?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bc37ea2e05019a89adaa48159b220483598d1898?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/21138/graphs/tree.svg?src=pr&width=650&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/21138?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #21138   +/-   ##
=======================================
  Coverage   91.84%   91.84%           
=======================================
  Files         153      153           
  Lines       49499    49499           
=======================================
  Hits        45460    45460           
  Misses       4039     4039
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <ø> (ø)` | :arrow_up: |
| #single | `41.88% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/21138?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/21138?src=pr&el=footer). Last update [bc37ea2...e9348b6](https://codecov.io/gh/pandas-dev/pandas/pull/21138?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks! thanks!