Remove AMR format parameter from AudioCoder in utility

The parameter was never used.

BUG=webrtc:3520

Review URL: https://codereview.webrtc.org/1365283002

Cr-Original-Commit-Position: refs/heads/master@{#10095}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: 8387c5f449c6cfcf6fe604489439efdb889e0c05
4 files changed