Remove old "bulletin board style toolbar" from core

Remove old "bulletin board style toolbar" from core

With this change, MediaWiki will no longer have a 'JavaScript-powered'
wikitext toolbar, and instead sysadmins will be required to choose one
(or more) of the several extensions available for this purpose if they
need the functionality. For over half a decade MediaWiki's tarball has
included the 2010-era replacement for this feature, WikiEditor. We are
now working on replacing even that, with the 2013-era visual editor, a
mode of which is the forthcoming 2017-era wikitext editor, and several
more specialised editors like CodeEditor.

Beyond this, the core editor toolbar is ancient, un-loved, and is used
only exceptionally rarely, mostly by accident. It is unhelpful to give
implicitly this as the primary editor for MediaWiki just because we've
not removed it from core when it is not a very good experience for any
kind of user, and has not received the attention that users deserve to
be worth retaining in core.

The old core preference, which was intended to govern whether this old
toolbar should be shown, has since mutated into whether the to run the
EditPageBeforeEditToolbar hook. The hook is used by several extensions
to provide toolbars in lieu of the core one. This preference has been,
in practice, a very confusing preference for MediaWiki users, who have
to interact with quite similar preferences to toggle their real editor
which sit next to this one on the preferences page. Consequently, this
preference is also removed.

The code could be made into an extension for those (very few) users of
MediaWiki who might want to keep on using it. However, the author will
offer their services but not their encouragement in said undertaking.

Bug: T30856
Bug: T32795
Change-Id: I2b05f0ca25873ad8e0b33a5e4938bef52c4e9347