DOC: suppress warnings for Panel4D deprecation
Other options is to just remove those sections in the latest docs ... (they are always available in the older ones).

The example in the HDF5 docs with a legacy file will have to be updated to not include Panel4D, or the reading of such files will have to be adapted in the future to handle those when Panel4D is actually removed (@jreback)

hmm I think removing them and pointing the old docs is better?

though the precedent is to leave them iirc (eg remote data)
 ## [Current coverage](https://codecov.io/gh/pydata/pandas/pull/13989?src=pr) is 85.28% (diff: 100%)

> Merging [#13989](https://codecov.io/gh/pydata/pandas/pull/13989?src=pr) into [master](https://codecov.io/gh/pydata/pandas/branch/master?src=pr) will decrease coverage by **<.01%**

``` diff
@@             master     #13989   diff @@
==========================================
  Files           139        139          
  Lines         50206      50206          
  Methods           0          0          
  Messages          0          0          
  Branches          0          0          
==========================================
- Hits          42818      42817     -1   
- Misses         7388       7389     +1   
  Partials          0          0          
```

> Powered by [Codecov](https://codecov.io?src=pr). Last update [29d9e24...7d067aa](https://codecov.io/gh/pydata/pandas/compare/29d9e24f4c778b0c9ebe9288bfc217808d2c6edb...7d067aace9dda76944c9a60ca8e9ca4ef0588562?src=pr)
 yep, will leave them in for now
