Clean up unneeded includes in common_audio/BUILD.gn.
Clean up unneeded includes in common_audio/BUILD.gn.

WebRTC internal headers are always included starting from the root
(e.g. #include "common_audio/..."), so there is no need to
specify the include_dirs removed by this CL.

Bug: webrtc:9538
Change-Id: Id2c070dad48c88dece3fea59e9dd0e64695ee298
Reviewed-on: https://webrtc-review.googlesource.com/89390
Reviewed-by: Oleh Prypin <5baa3e04f9bd6ba7a2a4b56625a3c84f19237cdb@webrtc.org>
Commit-Queue: Mirko Bonadei <d2c43c210eae6feef04f53bae50885e8152edcca@webrtc.org>
Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#24035}
TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,ShiftMediaProject/libilbc,ShiftMediaProject/libilbc,TimothyGu/libilbc,TimothyGu/libilbc