Correct conversion between float and fixed formats

This CL changes the way that values are converted
between fixed and floating point to
-Avoid the former asymmetric conversion causing
nonlinear distortions.
-Reduce the complexity.

Bug: webrtc:6594
Change-Id: I64d0cc31c5d16f397686a59a062cfbc4b336d94d
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/132783
Reviewed-by: Henrik Lundin <henrik.lundin@webrtc.org>
Reviewed-by: Gustaf Ullberg <gustaf@webrtc.org>
Commit-Queue: Per Åhgren <peah@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#28867}

common_audio/audio_util.cc

@@ -12,11 +12,6 @@
 
 namespace webrtc {
 
-void FloatToS16(const float* src, size_t size, int16_t* dest) {
-  for (size_t i = 0; i < size; ++i)
-    dest[i] = FloatToS16(src[i]);
-}
-
 void S16ToFloat(const int16_t* src, size_t size, float* dest) {
   for (size_t i = 0; i < size; ++i)
     dest[i] = S16ToFloat(src[i]);