Remove ignored return code from modules.

ModuleProcessImpl doesn't act on return codes and having them around is
confusing (it's unclear what an error return code here would do even).

BUG=
R=tommi@webrtc.org

Review URL: https://codereview.webrtc.org/1703833002 .

Cr-Commit-Position: refs/heads/master@{#11747}

webrtc/modules/bitrate_controller/include/mock/mock_bitrate_controller.h

@@ -36,7 +36,7 @@ class MockBitrateController : public BitrateController {
   MOCK_CONST_METHOD1(AvailableBandwidth, bool(uint32_t* bandwidth));
   MOCK_METHOD1(SetReservedBitrate, void(uint32_t reserved_bitrate_bps));
 
-  MOCK_METHOD0(Process, int());
+  MOCK_METHOD0(Process, void());
   MOCK_METHOD0(TimeUntilNextProcess, int64_t());
 };
 }  // namespace test