Issue #18492: Allow all resources when tests are not run by regrtest.py.

This changeset also includes cleanup allowed by this behavior change.
diff --git a/Lib/test/test_tk.py b/Lib/test/test_tk.py
index 56eef47..f3e264b 100644
--- a/Lib/test/test_tk.py
+++ b/Lib/test/test_tk.py
@@ -12,16 +12,10 @@
 with test_support.DirsOnSysPath(lib_tk_test):
     import runtktests
 
-def test_main(enable_gui=False):
-    if enable_gui:
-        if test_support.use_resources is None:
-            test_support.use_resources = ['gui']
-        elif 'gui' not in test_support.use_resources:
-            test_support.use_resources.append('gui')
-
+def test_main():
     with test_support.DirsOnSysPath(lib_tk_test):
         test_support.run_unittest(
             *runtktests.get_tests(text=False, packages=['test_tkinter']))
 
 if __name__ == '__main__':
-    test_main(enable_gui=True)
+    test_main()