configure: We don't want to clean configuration files

If you don't want to compile everything, you configure
config-devices.mak.  And then make clean remove it, and make will
create a default one without your configuration.  Fix it by not
removing it on clean target.  Remove it instead on distclean.

Signed-off-by: Juan Quintela <quintela@redhat.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>

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Remove it instead on distclean.