ClangTidy fixes for common_audio/

These are manual edits please verify there are no typos.
Feel free to auto-submit if there are no issues.

Bug: webrtc:10410
Change-Id: If995d9d9d21534d3c66a1e7c1fc1c62569766f40
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/127627
Commit-Queue: Benjamin Wright <benwright@webrtc.org>
Reviewed-by: Karl Wiberg <kwiberg@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#27138}
diff --git a/common_audio/audio_converter.cc b/common_audio/audio_converter.cc
index c560346..485ec80 100644
--- a/common_audio/audio_converter.cc
+++ b/common_audio/audio_converter.cc
@@ -20,8 +20,6 @@
 #include "rtc_base/checks.h"
 #include "rtc_base/numerics/safe_conversions.h"
 
-using rtc::checked_cast;
-
 namespace webrtc {
 
 class CopyConverter : public AudioConverter {
diff --git a/common_audio/sparse_fir_filter.cc b/common_audio/sparse_fir_filter.cc
index 0fc0327..772eb82 100644
--- a/common_audio/sparse_fir_filter.cc
+++ b/common_audio/sparse_fir_filter.cc
@@ -45,7 +45,7 @@
   }
 
   // Update current state.
-  if (state_.size() > 0u) {
+  if (!state_.empty()) {
     if (length >= state_.size()) {
       std::memcpy(&state_[0], &in[length - state_.size()],
                   state_.size() * sizeof(*in));
diff --git a/common_audio/wav_header.cc b/common_audio/wav_header.cc
index e49b748..9d602e9 100644
--- a/common_audio/wav_header.cc
+++ b/common_audio/wav_header.cc
@@ -122,7 +122,7 @@
     if (!readable->SeekForward(chunk_header->Size))
       return;  // EOF or error.
   }
-  return;  // EOF.
+  // EOF.
 }
 
 bool ReadFmtChunkData(FmtSubchunk* fmt_subchunk, ReadableWav* readable) {