fix(tests): tests/Makefile unnecessarily regenerates

tests/ruleset.am should not depend on the modification dates of the
*.rules files in the directory. 'bmake' (NetBSD make; also available in
some Linux distros) can occasionally treat 'ruleset.am' as outdated and
unnecessarily regenerates it, causing a chain of regeneration of
Makefiles or even dependency tracking error.

(This might look like a bug in bmake's side, but we should remove false
dependencies in makefiles anyway. 'ruleset.am' only depends on the names
and existences of the *.rules files, not their contents or modification
dates.)

tests/Makefile.am

@@ -434,7 +434,7 @@ RULESETS = \
 	$(srcdir)/yymorearraybol.rules \
 	$(srcdir)/yyunput.rules
 
-$(srcdir)/ruleset.am: $(srcdir)/ruleset.sh $(RULESETS)
+$(srcdir)/ruleset.am: $(srcdir)/ruleset.sh
 	( cd $(srcdir) && $(SHELL) ruleset.sh nr r c99 go >ruleset.am )
 
 include $(srcdir)/ruleset.am