Move audio_coding_module.gypi from main/acm2 to main/.

Prevents presubmit failures when touching audio_coding_module.gypi due
to source files being included from outside the gypi directory.

BUG=
R=minyue@webrtc.org

Review URL: https://codereview.webrtc.org/1262333002 .

Cr-Commit-Position: refs/heads/master@{#9659}
2 files changed