lfs: drop an unnecessary r'' prefix

No longer necessary since the source transformer was removed.

# skip-blame for changing string prefixes

Differential Revision: https://phab.mercurial-scm.org/D7958

hgext/lfs/blobstore.py

@@ -491,7 +491,7 b' class _gitlfsremote(object):'
                     hint=_(b'run hg verify'),
                 )
             request.data = lfsuploadfile(localstore.open(oid))
-            request.get_method = lambda: r'PUT'
+            request.get_method = lambda: 'PUT'
             request.add_header('Content-Type', 'application/octet-stream')
             request.add_header('Content-Length', len(request.data))