(bug 40632) Remove CleanupPresentationalAttributes feature

(bug 40632) Remove CleanupPresentationalAttributes feature

Removed $wgCleanupPresentationalAttributes, the associated
code it toggles and references to those in src and tests.

Also fixes bug 40329.

This was originally introduced in r94465 (released in REL1_19) but
disabled by default. Then enabled in r98053, after which several
bugs were filed and eventually the decision was made to remove
this feature.

Removed obsolete release-note entry, as this is to be backported
to REL1_20.

Change-Id: I4e86305520a3b22ef88381caab55d24abac932e3