tests: Replace umodule with module everywhere.

This work was funded through GitHub Sponsors.

Signed-off-by: Jim Mussared <jim.mussared@gmail.com>

tests/basics/io_stringio_with.py

@@ -1,8 +1,4 @@
-try:
-    import uio as io
-except ImportError:
-    import io
-
+import io
 # test __enter__/__exit__
 with io.StringIO() as b:
     b.write("foo")