d/rules: drop doc binary cleanup

The new doc build does not trigger the old problem.
Remove the cleanup:
While being still built for example:
./build/examples/c/domain/suspend.o
./build/examples/c/domain/suspend
They are no more ending up in the docs:
$ find libvirt-doc/usr/share/doc/libvirt-doc/examples/ -name "*suspend*"
libvirt-doc/usr/share/doc/libvirt-doc/examples/c/domain/suspend.c

Same for the other file (types) that we cleaned.

Signed-off-by: Christian Ehrhardt <christian.ehrhardt@canonical.com>