Don't remove depend with a make clean

otherwise you'll get a regeneration of the dependency file for each clean command
which is useless.
make distclean shall be used to remove the dependency file.

tests/Makefile

@@ -60,9 +60,9 @@ check: depend
 clean:
 	$(RM) *.exe *.s *~ *.o *.log *.valgrind ./a*.dat clang_output_* *.c.c *.end.c *.first.c *.middle.c
 	$(RM) -rf coverage *.gcda *.gcno *.gcov all.info test.tar coverage-dir mlib-report *.synt
-	$(RM) *.depend depend
 
 distclean: clean
+	$(RM) *.depend depend
 
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 # Code generation analysis