Drop PTE check in pmap_fault_fixup(). Since pmap_enter() doesn't

Drop PTE check in pmap_fault_fixup().  Since pmap_enter() doesn't
add PTE's for pages that haven't been accessed yet, the check would
skip the fixup on such pages and force us to go through uvm_fault()
just for the sake of MOD/REF bit emulation.  Since we already check
the PTE descriptor, dropping the check should be safe.  Doing so
gives us a nice 10% performance gain when building a kernel.

ok patrick@, drahn@