Deprecated unnecessary gwpy.utils.compat module
This PR deprecates (but doesn't remove) the gwpy.utils.compat module which so far only provided an import for OrderedDict. Since we don't support python2.6 anymore, we don't need it.
This PR deprecates (but doesn't remove) the gwpy.utils.compat module which so far only provided an import for OrderedDict. Since we don't support python2.6 anymore, we don't need it.