malloc: Remove check_action variable [BZ #21754]

Clean up calls to malloc_printerr and trim its argument list.

This also removes a few bits of work done before calling
malloc_printerr (such as unlocking operations).

The tunable/environment variable still enables the lightweight
additional malloc checking, but mallopt (M_CHECK_ACTION)
no longer has any effect.

(cherry-picked from ac3ed168)