Backout previous "Unwire with map lock held" (commitid: eQBvWUwShD91dN9Z)

Backout previous "Unwire with map lock held" (commitid: eQBvWUwShD91dN9Z)

WITNESS builds broke^W^Wkernels panic on boot as reported by anton and bluhm.
Booting bsd.mp in single-user mode inside VMM shows:

root on sd0a (5f9e458ed30b39ab.a) swap on sd0b dump on sd0b
Enter pathname of shell or RETURN for sh:
witness: lock order reversal:
 1st 0xfffffd801f8ce468 vmmaplk (&map->lock)
 2nd 0xfffffd801b8162c0 inode (&ip->i_lock)
lock order "&ip->i_lock"(rrwlock) -> "&map->lock"(rwlock) first seen at:
#0  rw_enter_read+0x38
#1  uvmfault_lookup+0x8a
#2  uvm_fault_check+0x32
#3  uvm_fault+0xfb
#4  kpageflttrap+0x12c
#5  kerntrap+0x91
#6  alltraps_kern_meltdown+0x7b
#7  copyout+0x53
#8  ffs_read+0x1f6
#9  VOP_READ+0x41
#10 vn_rdwr+0xa1
#11 vmcmd_map_readvn+0xa0
#12 exec_process_vmcmds+0x88
#13 sys_execve+0x732
#14 start_init+0x26f
#15 proc_trampoline+0x1c
lock order data w1 -> w2 missing
# exit
kernel: protection fault trap, code=0
Stopped at      witness_checkorder+0x312:       movl    0x10(%r14),%ecx

gkoehler reported faults on poisened addresses on macppc dual G5.