Issue #19587: Remove masked and redundant tests in test_bytes

* test_contains() did not override anything
* test_expandtabs/upper/lower() in FixedStringTest were masking usable tests
  in string_tests. These tests now get run for bytearray() and bytes().
* test_expandtabs/upper/lower() in buffer_tests were only run on bytearray()
  and are redundant with string_tests