test-atomic: Drop atomic read-modify-write tests for the moment.

test-atomic: Drop atomic read-modify-write tests for the moment.

XenServer builds are failing because of link errors reporting that
__sync_fetch_and_<op>_<size> were not found, for <op> in add/sub/and/xor/or
and <size> in 1/2/4/8.  We're not actually using these RMW operations yet,
so as a stopgap measure just drop the tests.

The correct long-term fix is probably to do Autoconf linkage tests for
these operations instead of just testing the GCC version (if we really need
the operations at all).

Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Ethan Jackson <ethan@nicira.com>