mediawiki.legacy.ajax: Pass JSHint
* Added closure so that "mw.util.wikiScript" doesn't access
global "mw" directory but uses local reference to global
"mediaWiki".
* Keps names as-is, as such disabled camelcase rule locally
for this file. This code will be wrap-deprecated and removed
over the next 2 releases.
* Turned into local cross-references and exposed those, that
way the individual methods don't all call implied globals but
are ensured to be referring to the original methods as they
were defined in the same scope.
* Fixed clashing 'e' variable name.
* Removed unexpected "delete x" statement. Does nothing and
causes a lint warning.
* Replaced "delete request" with "request = undefined". The
purpose of the statement is to explicitly dereference the
XHR object in older IE browsers. However "delete" is not
allowed for local varables, setting to undefined has the
same effect.
* Moved debug_mode and request_type down to the other exposures.
Change-Id: Ib45ed9bd8c6f4ebdb060a527a63eaf59d2839493