misc: Provide a uninstall-hook to remove the extra files

Fix make distcheck to uninstall files that were installed
by our custom hook.

This is fixing:
ERROR: files left after uninstall:
./share/doc/openbsc/examples/osmo-bsc_mgcp/mgcp.cfg
./share/doc/openbsc/examples/osmo-nitb/nanobts/openbsc.cfg
./share/doc/openbsc/examples/osmo-nitb/nanobts/openbsc-multitrx.cfg
./share/doc/openbsc/examples/osmo-nitb/bs11/openbsc-1bts-2trx.cfg
./share/doc/openbsc/examples/osmo-nitb/bs11/openbsc.cfg
./share/doc/openbsc/examples/osmo-nitb/bs11/openbsc-1bts-2trx-hopping.cfg
./share/doc/openbsc/examples/osmo-nitb/bs11/openbsc-2bts-2trx.cfg
./share/doc/openbsc/examples/osmo-nitb/rbs2308/openbsc.cfg
1 file changed
tree: 10723e3c80ea3fdac01cda35a0505575b68c7afd
  1. hlrsync/
  2. linux-kernel/
  3. openbsc/
  4. wireshark/
  5. README