t/Makefile: remove 'test-results' on 'make clean'

The 't/test-results' directory and its contents are by-products of the test process, so 'make clean' should remove them, but, alas, this has been broken since fee65b194d (t/Makefile: don't remove test-results in "clean-except-prove-cache", 2022-07-28). The 'clean' target in 't/Makefile' was not directly responsible for removing the 'test-results' directory, but relied on its dependency 'clean-except-prove-cache' to do that [1]. ee65b194d broke this, because it only removed the 'rm -r test-results' command from the 'clean-except-prove-cache' target instead of moving it to the 'clean' target, resulting in stray 't/test-results' directories. Add that missing cleanup command to 't/Makefile', and to all sub-Makefiles touched by that commit as well. [1] 60f26f6348 (t/Makefile: retain cache t/.prove across prove runs, 2012-05-02) Signed-off-by: SZEDER Gábor <szeder.dev@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>