Makefile: remove UNIT_TEST_BIN directory with "make clean"

We remove $(UNIT_TEST_PROGS), but that leaves the automatically
generated "bin" dir they reside in. And once we start cleaning that,
there is no point in removing the individual programs, as they'll by
wiped out by the recurse "rm".

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Makefile

@@ -3676,14 +3676,14 @@ cocciclean:
 	$(RM) contrib/coccinelle/*.cocci.patch
 
 clean: profile-clean coverage-clean cocciclean
-	$(RM) -r .build
+	$(RM) -r .build $(UNIT_TEST_BIN)
 	$(RM) po/git.pot po/git-core.pot
 	$(RM) git.res
 	$(RM) $(OBJECTS)
 	$(RM) headless-git.o
 	$(RM) $(LIB_FILE) $(XDIFF_LIB) $(REFTABLE_LIB) $(REFTABLE_TEST_LIB)
 	$(RM) $(ALL_PROGRAMS) $(SCRIPT_LIB) $(BUILT_INS) $(OTHER_PROGRAMS)
-	$(RM) $(TEST_PROGRAMS) $(UNIT_TEST_PROGS)
+	$(RM) $(TEST_PROGRAMS)
 	$(RM) $(FUZZ_PROGRAMS)
 	$(RM) $(SP_OBJ)
 	$(RM) $(HCC)