tests: Bluetooth: tester: Fix assert in OTS

MCS OTS support doesn't implement OTS checksum and if this is globally
enabled assert is triggered.

[00:00:03.409,484] <dbg> bttester_gap: set_io_cap: io_cap: 0
ASSERTION FAIL [ots_init->cb->obj_cal_checksum]
     @ WEST_TOPDIR/zephyr/subsys/bluetooth/services/ots/ots.c:476
 Callback for object calculate checksum is not set

This should be reverted when Zephyr issue #72471 is fixed.

Signed-off-by: Szymon Janc <szymon.janc@codecoup.pl>