Removed used copies of ../mount/getmntopts.c ../mount/mntopts.h. Use the
versions in ../mount directly like all other mount utilities.
Removed used copy of ../mount/pathnames.h. Use the version in ../mount
for free as a side effect of using the mntopts files there. We should
not use it at all, since the 2/3 of the definitions in it are in <paths.h>
and the other 1/3 should be in ../mountd/pathnames.h and is not used by
mount_ifs anyway.