API: Remove action=paraminfo 'props' and 'errors' result properties

The format for 'props' was never specified and the list for 'errors' is
impossible to keep updated when considering that many errors come from
MediaWiki backend code and extension hook functions. And since there
doesn't seem to be any real use case for either of these, let's just
kill both of them instead of wasting effort on trying to fix them.

Note that neither getResultProperties nor getPossibleErrors are called
from any extensions in gerrit, and none of the other deprecated methods
are called outside of the implementations of those two methods. Removing
the obsolete methods is left to the maintainers of the extensions, as
keeping them hurts nothing and is needed to maintain compatibility with
earlier versions of MediaWiki.

Change-Id: Ie11a401d60c834059fbf1b5625ca8ea093b3337c
Merge "API: Remove action=paraminfo 'props' and 'errors' result properties"