MB: Cleanup no-longer-used GN configurations
MB: Cleanup no-longer-used GN configurations

These were used in the transition from GN->GYP.

NOTRY=True
BUG=webrtc:5949

Review-Url: https://codereview.webrtc.org/2310973003
Cr-Original-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#14087}
Cr-Mirrored-From: https://chromium.googlesource.com/external/webrtc
Cr-Mirrored-Commit: dedc822830f9013927afb9bf36acd03d2fc859cf

Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk,Alkalyne/webrtctrunk