Removed Die mock from MockAudioEncoder

MockAudioEncoder was calling a mocked Die function on itself in its
destructor. This outputs "Uninteresting mock function call" warning if
the Die call was not expected. This is true even if a NiceMock is used
to suppress the warnings.

The purpose of testing that the destructor is called might be to protect
against memory leaks when audio encoder ownership is transferred using a
raw pointer. However, this case is already covered by msan checks.

Bug: None
Change-Id: I0603c417b4b239027859228e05ebcf83ff5aaf18
Reviewed-on: https://webrtc-review.googlesource.com/56183
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Commit-Queue: Sebastian Jansson <srte@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#22146}

api/audio_codecs/test/audio_encoder_factory_template_unittest.cc

@@ -65,7 +65,6 @@ struct AudioEncoderFakeApi {
     auto enc = rtc::MakeUnique<testing::StrictMock<MockAudioEncoder>>();
     EXPECT_CALL(*enc, SampleRateHz())
         .WillOnce(testing::Return(Params::CodecInfo().sample_rate_hz));
-    EXPECT_CALL(*enc, Die());
     return std::move(enc);
   }
 };