core-image-sato-sdk-ptest: do not pull in ptest-pkgs

core-image-sato-sdk-ptest: do not pull in ptest-pkgs

The lists of ptests are defined via PTESTS_FAST and PTESTS_SLOW;
specifying 'ptests-pkgs' also pulls in additional ptests that
are specifically excluded from those lists due to causing issues with
ptesting. (particularly bash-ptest is one such item)

Signed-off-by: Alexander Kanavin <alex.kanavin@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>