Remove test galera.galera_bf_abort_group_commit

Test galera_bf_abort_group_commit was re-enabled (by mistake?) in commit 0174a9ff3d412ada22205edc19066a14c52d6e99, and has been failing since then.
The test is configured is configured to run with commit order disabled, a configuration which is which meant for testing performance penalty of commit ordering.
Moreover, we have test galera_sr.galera_sr_bf_abort, which is identical but it runs with commit ordering enabled.
No reason to keep the failing test around.