mklib, upas/common: clean up libcommon properly (thanks mikan)

Despite pervious efforts, mk clean still doesn't remove libcommon.a*
files from cmd/upas/common/. To fix this, let's tell cmd/mklib to do
the job instead.

sys/src/cmd/mklib

@@ -39,7 +39,7 @@ nuke:V:
 	rm -f *.[$OS] y.tab.? y.output y.error $CLEANFILES $LIB
 
 clean:V:
-	rm -f *.[$OS] y.tab.? y.output y.error $CLEANFILES
+	rm -f *.[$OS] *.a[$OS] y.tab.? y.output y.error $CLEANFILES
 
 %.acid:V:
 	$CC $CFLAGS -a `{basename $stem .$objtype}^.c >$target

sys/src/cmd/upas/common/mkfile

@@ -15,6 +15,4 @@ HFILES=\
 	common.h\
 	sys.h\
 
-CLEANFILES=libcommon.a[$OS]
-
 </sys/src/cmd/mklib