Makefile: speed fastcheck

Rather than timeout, explicitly disable tests_pass_valgrind and
tests_compile_coverage.  This is important now we run under valgrind
the first time we run the tests, thus would always time out and not
run most of the tests at all!

"make check" takes 7m57s, old "make fastcheck" takes 3m28s, and this takes
only 1m57s, but much more is run (as shown by the larger score total).

Makefile

@@ -101,7 +101,7 @@ summary-check-%: tools/ccanlint/ccanlint $(OBJFILES)
 	tools/ccanlint/ccanlint -s -d ccan/$*
 
 summary-fastcheck-%: tools/ccanlint/ccanlint $(OBJFILES)
-	tools/ccanlint/ccanlint -t $(FASTTIMEOUT) -s -d ccan/$*
+	tools/ccanlint/ccanlint -x tests_pass_valgrind -x tests_compile_coverage -s -d ccan/$*
 
 ccan/%/info: ccan/%/_info
 	$(CC) $(CCAN_CFLAGS) -o $@ -x c $<