Remove vigeni@ from OWNERS.

The email address is no longer valid and thus shouldn't be listed as an owner.

Change-Id: Ic20a4e4248c1802050a19f0fc8f7c1cf5255c839
Reviewed-on: https://chromium-review.googlesource.com/c/cast_core/public/+/6886689
Tested-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Shawn Quereshi <shawnq@google.com>