Avoid duplicate accesskey hints on OOUI widgets

Avoid duplicate accesskey hints on OOUI widgets

Values returned by `Linker::tooltipAndAccesskeyAttribs()` and
`Linker::titleAttrib( ..., 'withaccess' )` include an accesskey
hint in the title text. This is unnecessary when used for OOjs UI
widgets, since after the changes from T168408 they display an
accesskey hint automatically.

Also fixed some other accesskey bugs in HTMLForm which probably
no one ever ran into.

Bug: T168408
Change-Id: I63285b5bce3341875a6d82eba059623bf105ca62