Remove useless copyright pre-commit hook (PaddlePaddle#380)

* remove copyright hook

Author: ZeyuChen

.copyright.hook

@@ -30,12 +30,3 @@
         -   --show-source
         -   --statistics
         files: \.py$
-
--   repo: local
-    hooks:
-    -   id: copyright_checker
-        name: copyright_checker
-        entry: python ./.copyright.hook
-        language: system
-        files: \.(c|cc|cxx|cpp|cu|h|hpp|hxx|proto|py)$
-        exclude: (?!.*third_party)^.*$