qca-wifi: Remove references to CHAN_NUM_API

During 6G development, CONFIG_CHAN_NUM_APIs are kept for backward
compatability. Remove CONFIG_CHAN_NUM_API macro and remove all the
references to any function defined/declared under the macro.

CRs-Fixed: 2711597
Change-Id: Iac5d57e4e0fb1fa54b0225a5cb206e8f1fe1353d