Revert "OS-8005 bhyve memory pressure needs to target ARC better (#354)"
This reverts commit a6033573eedd94118d2b9e65f45deca0bf4b42f7.

*** 1580,1596 ****
                  memflags |= VM_MEM_F_INCORE;
          vm_set_memflags(ctx, memflags);
  #ifdef  __FreeBSD__
          err = vm_setup_memory(ctx, memsize, VM_MMAP_ALL);
  #else
-         err = vm_arc_resv(ctx, memsize);
-         if (err != 0) {
-                 (void) fprintf(stderr, "Could not shrink ARC: %s\n",
-                     strerror(err));
-                 exit(4);
-         }
- 
          do {
                  errno = 0;
                  err = vm_setup_memory(ctx, memsize, VM_MMAP_ALL);
                  error = errno;
                  if (err != 0 && error == ENOMEM) {
--- 1580,1589 ----