Tiny doc grammar fix: remove redundant "for"

(cherry picked from commit 6faeb3f)

asyncprawcore/auth.py

@@ -53,7 +53,7 @@ def authorize_url(self, duration, scopes, state, implicit=False):
         :param state: A string that will be reflected in the callback to
             ``redirect_uri``. Elements must be printable ASCII characters in the range
             0x20 through 0x7E inclusive. This value should be temporarily unique to the
-            client for whom the URL was generated for.
+            client for whom the URL was generated.
         :param implicit: (optional) Use the implicit grant flow (default:
             False). This flow is only available for UntrustedAuthenticators.