Check usages of isAztecEditorEnabled and isGutenbergEditorEnabled

[malinajirka]

Audit PostUtils.isAztecEditorEnabled and PostUtils.isGutenbergEditorEnabled as per #10798 (comment).

[jd-alexander]

Heads up that I am doing an audit of several tickets in this repo that has been opened for a long time and this is an item in this list. If this helps, we have disabled the option to switch to the classic editor #14334 and we have added a deprecation notice for our users #14205 so the classic editor is primarily available for viewing older posts made within it since the block editor isn't able to edit them.