Eliminated the skipna / dropna inconsistency in the docs.


As @bf mentioned in the comments under the  issue #34063 ,
There are errors in the docs for Dataframe.mode, https://pandas.pydata.org/pandasdocs/dev/reference/api/pandas.DataFrame.mode.html (See source : https://github.com/pandas-dev/pandas/blob/master/pandas/core/frame.py#L8722-L8807) , where the dropna parameter (which occurs more number of times than skipna) has been named skipna (first occurrence on line 8370).  
Thanks @ashwinpn 

Changing all `skipna`s to `dropna`s would be a pretty big API change, are you sure it would be worth it? @MarcoGorelli yes, you are correct - That is why I have currently kept this as a draft, it might not be worth it.  Thanks for the PR. In theory I think there are cases where these would signal distinct functionality though there are other functions where they overlap and maybe could be aligned.However, this isn't something we would just change outright - would need to go through a deprecation cycle first for any changes. 

I think if something you want to pursue its worth starting with an issue and discussion before a PR. We would need to align further on goal and functions where maybe this makes sense