This reverts "iOS: Add mb_type config for GYP builders."
and also removes Goma from these builders, as it will not work for WebRTC
since MB's GYP mode is hardcoded to use gyp_chromium.
MB should be working for GN since it's a stand-alone tool.
Goma doesn't work since $(goma_dir) in the JSON throws an error during
compile. So let's turn off Goma for these bots for now.
BUG=chromium:498746
NOTRY=True
TBR=smut@google.com
Review URL: https://codereview.webrtc.org/1685683007
Cr-Commit-Position: refs/heads/master@{#11578}
d3d8b6720a