tests/prime_busy: Remove unstable sub-test from BAT/add flag to bring them back when they're stable to be run in CI.

The following BAT are causing problems:

prime_busy@basic-after-default, fails on all platforms
since it was added, and it sometimes hangs BSW machine
prime_busy@basic-before-default, fails on all platforms
since it was added.
prime_busy@basic-wait-after-default, fails on all platforms
since it was added, and it sometimes hangs BSW machine
prime_busy@basic-wait-before-default, fails on all platforms
since it was added.

Signed-off-by: Marius Vlad <marius.c.vlad@intel.com>