chromium: Drop obsolete pre-v23 seccomp patch.

The patch is no longer needed, as we are now using the BPF seccomp sandbox.
Unfortunately this is not marked "adequately sandboxed" in chrome://sandbox, as
it awaits security review on http://crbug.com/26528

.

Unfortunately this gets us into a position where we can't be sure if the sandbox
is working correctly, especially because the non-BPF seccomp sandbox has a bunch
of stability issues and is marked legacy. And we definitely don't want to add
support for the setuid sandbox, do we?

Signed-off-by: aszlig <aszlig@redmoonstudios.org>