Revert of Enable GN check for webrtc/examples (patchset #7 id:120001 of https://codereview.webrtc.org/2714343002/ )

Reason for revert:
I wasn't able to resolve it with that CL so I'll have to revert this by now.

Will have another look at this when time permits.

Original issue's description:
> Enable GN check for webrtc/examples
>
> BUG=webrtc:6828
> NOTRY=True
>
> Review-Url: https://codereview.webrtc.org/2714343002
> Cr-Commit-Position: refs/heads/master@{#16987}
> Committed: https://chromium.googlesource.com/external/webrtc/+/81db74a3841b42c0a84c2f35b91eab66fd3f4e79

TBR=perkj@webrtc.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=webrtc:6828

Review-Url: https://codereview.webrtc.org/2727253003
Cr-Commit-Position: refs/heads/master@{#16991}