Get channels info from wificond

This removes the code for supporting HAL based
getChannelsForBand().
This also plumbs all the existing usage of that
method to wificond based implementation.

Bug: 35707768
Test: compile, unit tests
Test: manual test that this new API is called and returns
expected values by inserting logs.

Change-Id: Ie193ab3f8591664afb12bd6234f49e762ab7fc4d
9 files changed