Using "libtool --clean" to remove regular files is slow.

We only need to use libtool's clean mode to remove files created by libtool.

plugins/python/Makefile.in

@@ -185,8 +185,8 @@ pvs-studio: $(POBJS)
 check:
 
 clean:
-	-$(LIBTOOL) $(LTFLAGS) --mode=clean rm -f *.lo *.o *.la *.a *.i *.plog \
-	    stamp-* core *.core core.*
+	-$(LIBTOOL) $(LTFLAGS) --mode=clean rm -f *.lo *.o *.la
+	-rm -f *.i *.plog stamp-* core *.core core.*
 
 mostlyclean: clean