powerpc64/pmap: No need for moea64_pvo_remove_from_page_locked() wrapper

The only consumer of moea64_pvo_remove_from_page_locked() already has the
page in hand, so there is no need to search for the page while holding the
lock. Drop the wrapper, and rename _moea64_pvo_remove_from_page_locked().

Reported by: alc