cmake: Don't install chrome manifest to ubuntu specific location

Ubuntu patches their chromium to have extension path to be
chromium-browser/extensions instead of chromium/extensions for whatever
reasons. This doesn't work with anything !ubuntu.

So code here is adjusted to match what upstream does for now, ubuntu
needs to manually patch this out OR devise a packaging level solution as
we can't keep packaging workarounds in upstream repository.

BUG: 393846

Reviewed-by: kbroulik

CCMAIL: distributions@kde.org
CCMAIL: kde-distro-packagers@kde.org