oops, fix FileOp::RenameOp to use physpath (the compiler didn't
catch this one because the API didn't change).

retire find_all_expansions(), no longer used.
i forgot to remove adplfs_num_host_dirs() a while ago (in the
iostore changes), it is no longer used.
missed a couple of PLFS_EXITs
- replace stripPrefixPath() with skipPrefixPath().   does the same
  basic thing, but with less overhead (no need to malloc strings or
  allocate PATH_MAX on the stack).

- retire find_mount_point_using_tokens(), expandPath(), and ExpansionInfo