ZTS: Update enospc_002_pos test case
The on-disk cost of creating a snapshot or bookmark is sufficiently low
that it is difficult to make it reliably fail even when the pool is
"full". In order to avoid false positives remove these two checks from
the test case.
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #13060