CHORMIUM: ath10k: Remove obsoleted code in ath10k_mac_update_airtime()

Remove the obsoleted code that handles broadcast and multicast frames in
ath10k_mac_update_airtime(). The current version of airtime fairness
based tx scheduler does not apply to broadcast and multicast frame.

BUG=b:131197056
TEST=None

Signed-off-by: Kan Yan <kyan@google.com>
Change-Id: If27c7ad458a85553b3e34810bf12c0120005bd5d
Reviewed-on: https://chromium-review.googlesource.com/1746757


Tested-by: Kan Yan <kyan@chromium.org>
Commit-Ready: Kan Yan <kyan@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Danny Mitzel <mitzel@google.com>
Reviewed-by: Danny Mitzel <mitzel@chromium.org>
Reviewed-by: Rajkumar Manoharan <rmanohar@qualcomm.corp-partner.google.com>
Reviewed-by: Julan Hsu <julanhsu@google.com>
Reviewed-by: Kan Yan <kyan@chromium.org>