Remove broken _reprcompare disabling fixture in test_assertrewrite.py

The `_pytest._code._reprcompare` that was referred to previously doesn't
exist -- it was moved to other places but wasn't updated. This regressed
in f423ce9c01. Now we don't want it
anymore, so keep the status quo by explicitly removing them.

testing/test_assertrewrite.py

@@ -25,16 +25,6 @@ from _pytest.config import ExitCode
 from _pytest.pathlib import Path
 
 
-def setup_module(mod):
-    mod._old_reprcompare = util._reprcompare
-    _pytest._code._reprcompare = None
-
-
-def teardown_module(mod):
-    util._reprcompare = mod._old_reprcompare
-    del mod._old_reprcompare
-
-
 def rewrite(src):
     tree = ast.parse(src)
     rewrite_asserts(tree, src.encode())