Remove duplicate flake8 ignore config

Summary:
Hi, thanks a lot for sharing this amazing project. While I was reading the code, I found there is a duplicate flake8 ignore config. This PR is to remove the duplicate item. Thanks.

Pull Request resolved: #3132

Reviewed By: theschnitz

Differential Revision: D29349703

Pulled By: ppwwyyxx

fbshipit-source-id: e2047647c360482047051579e5d855597eba573a

Author: firstmover

.flake8

@@ -2,7 +2,7 @@
 # Keep in sync with setup.cfg which is used for source packages.
 
 [flake8]
-ignore = W503, E203, E221, C901, C408, E741, C407, E741, B017
+ignore = W503, E203, E221, C901, C408, E741, C407, B017
 max-line-length = 100
 max-complexity = 18
 select = B,C,E,F,W,T4,B9