Delete a few unused methods on DecoderDatabase

Bug: none
Change-Id: Ic0a20036b92e0f1d088bae88724a777eca93760d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/262763
Reviewed-by: Minyue Li <minyue@webrtc.org>
Commit-Queue: Niels Moller <nisse@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#36924}

modules/audio_coding/neteq/mock/mock_decoder_database.h

@@ -27,7 +27,6 @@ class MockDecoderDatabase : public DecoderDatabase {
   MOCK_METHOD(void, Die, ());
   MOCK_METHOD(bool, Empty, (), (const, override));
   MOCK_METHOD(int, Size, (), (const, override));
-  MOCK_METHOD(void, Reset, (), (override));
   MOCK_METHOD(int,
               RegisterPayload,
               (int rtp_payload_type, const SdpAudioFormat& audio_format),