Remove -test-name in favor of test runner option

`-define:ODIN_TEST_NAMES=...` is capable of selecting test by package
and name or name only, with the ability to access packages included by
`-all-packages`.

src/build_settings.cpp

@@ -893,7 +893,6 @@ struct BuildContext {
 	u32 cmd_doc_flags;
 	Array<String> extra_packages;
 
-	StringSet test_names;
 	bool      test_all_packages;
 
 	gbAffinity affinity;