Refactor and cleanup codes. No functional changes.

common/python/rsa_key.clif

@@ -0,0 +1,15 @@
+################################################################################
+# Copyright 2018 Google LLC.
+#
+# This software is licensed under the terms defined in the Widevine Master
+# License Agreement. For a copy of this agreement, please contact
+# widevine-licensing@google.com.
+################################################################################
+
+from "common/rsa_key.h":
+  namespace `widevine`:
+    class RsaPublicKey:
+      def VerifySignature(self, message: bytes, signature: bytes) -> bool
+
+    staticmethods from `RsaPublicKey`:
+      def Create(serialized_key: bytes) -> RsaPublicKey