assistant: Fix invalid use of std::move

Bug: 981365
Test: manual
Change-Id: I9d6b3838ee5d641f20b51e0e34810e788c1e24e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1696523
Commit-Queue: Tao Wu <wutao@chromium.org>
Reviewed-by: Xiaohui Chen <xiaohuic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#676615}

chromeos/services/assistant/platform/audio_stream_handler.cc

@@ -112,7 +112,7 @@ void AudioStreamHandler::OnDecoderInitializedOnThread(
     if (!stopped_)
       OnError(assistant_client::AudioOutput::Error::FATAL_ERROR);
 
-    std::move(start_device_owner_on_main_thread_);
+    start_device_owner_on_main_thread_.Reset();
     return;
   }
 
@@ -169,7 +169,7 @@ void AudioStreamHandler::FillDecodedBuffer(void* buffer, int buffer_size) {
 void AudioStreamHandler::OnFillBufferOnThread(
     assistant_client::Callback1<int> on_filled,
     int num_bytes) {
-  std::move(on_filled)(num_bytes);
+  on_filled(num_bytes);
 }
 
 void AudioStreamHandler::DecodeOnThread() {