Revert r349442, which was a workaround for bus errors caused by an errant
TLB entry. Specifically, at the start of pmap_enter_quick_locked(), we
would sometimes have a TLB entry for an invalid PTE, and we would need to
issue a TLB invalidation before exiting pmap_enter_quick_locked(). However,
we should never have a TLB entry for an invalid PTE. r349905 has addressed
the root cause of the problem, and so we no longer need this workaround.

X-MFC after: r349905