Revert serie of "EditPage: Use context instead of globals"

Reverts:

89cade EditPage: Use context instead of globals (4/4)
27fd110 EditPage: Use context instead of globals (3/4)
afa6307 EditPage: Use context instead of globals (2/4)
f2f8101 EditPage: Use context instead of globals (1/4)

LiquidThreads is still using globals when invoking EditPage. That can be
reproduced by attempting to reply to a message which eventually causes
EditPage::importFormData() to errors out with:

ErrorPageError from includes/EditPage.php:
The content format json is not supported by the content model wikitexte.

Bug: T143889
Change-Id: I593450971e4a4a31c88df49334859508d1fd006c

diff --cc includes/EditPage.php
Simple merge