Fix compile failure

commit 884866b3 introduces a compile
failure,

make[3]: *** No rule to make target `lock.c', needed by `liblxc_so-lock.o'.  Stop.
make[3]: Leaving directory `/home/dhaval/work/lxc/lxc/src/lxc'
make[2]: *** [all-recursive] Error 1
make[2]: Leaving directory `/home/dhaval/work/lxc/lxc/src'
make[1]: *** [all] Error 2
make[1]: Leaving directory `/home/dhaval/work/lxc/lxc/src'
make: *** [all-recursive] Error 1

Remove those entries from the Makefile
Signed-off-by: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Signed-off-by: Daniel Lezcano <dlezcano@fr.ibm.com>