Remove unused codes from ext and ounit_tests (#7381)

Author: cometkim

compiler/bsc/rescript_compiler_main.ml

@@ -454,8 +454,5 @@ let _ : unit =
     Format.eprintf "%s@." msg;
     exit 2
   | x ->
-    (*
-        Ext_obj.bt ();
-*)
     Location.report_exception ppf x;
     exit 2

compiler/ext/ext_js_regex.ml

@@ -8,16 +8,13 @@ let suites =
       Ounit_scc_tests.suites;
       Ounit_list_test.suites;
       Ounit_hash_set_tests.suites;
-      Ounit_union_find_tests.suites;
       Ounit_bal_tree_tests.suites;
       Ounit_hash_stubs_test.suites;
       Ounit_map_tests.suites;
       Ounit_hashtbl_tests.suites;
       Ounit_string_tests.suites;
-      Ounit_topsort_tests.suites;
       Ounit_int_vec_tests.suites;
       Ounit_ident_mask_tests.suites;
-      Ounit_js_regex_checker_tests.suites;
       Ounit_utf8_test.suites;
       Ounit_unicode_tests.suites;
       Ounit_bsb_regex_tests.suites;