kernel: drop unused priority related definitions

There are no reference for either K_NUM_PRIORITIES or
K_NUM_PRIO_BITMAPS, with the former being dropped in:

  1acd8c2996 kernel: Scheduler rewrite

Dropping both of these, and also the two comments about extra priorities
taking extra RAM space, as those do not seem to apply either.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>
2 files changed