Fix some out-of-sync differences between GYP and GN targets for
desktop capture.
Remove sources that aren't used on iOS for that platform, to solve
linking errors that surfaced when flipping iOS to GN by default.
BUG=webrtc:5949
NOTRY=True
TBR=sergeyu@chromium.org
Review-Url: https://codereview.webrtc.org/2289103002
Cr-Commit-Position: refs/heads/master@{#13971}