CLEANUP: http_ana: remove unused assignation of att_beg

`att_beg` is assigned to `next` at the end of the `for` loop, but is
assigned to `prev` at the beginning of the loop, which is itself
assigned to `next` after each loop. So it represents a double
assignation for the same value. Also `att_beg` is not used after the end
of the loop.

this is a partial fix for github issue #923, all the others could
probably be marked as intentional to protect future changes.

no backport needed.

Signed-off-by: William Dauchy <wdauchy@gmail.com>

src/http_ana.c

@@ -3533,8 +3533,6 @@ static void http_manage_client_side_cookies(struct stream *s, struct channel *re
 				}
 			}
 
-			/* continue with next cookie on this header line */
-			att_beg = next;
 		} /* for each cookie */