SECURITY: Prevent tokens in jsonp mode

Add checks to token-returning functions to prevent returning tokens in
jsonp mode. This affects action=tokens, action=login,
action=createaccount, and action=query&list=deletedrevs.

Also, remove the "gettoken" parameter to action=block and
action=unblock, which has been deprecated since 1.20.

Bug: 49090
Change-Id: Ibeaa5c72d8084585092b15935a3f5709104bf7f7