WPS: Remove unused Credential AP Channel processing

WPS: Remove unused Credential AP Channel processing

Commit bd3a3737672aaf6eb50dba2b8caa3941c8df42e9 added a mechanism to use
AP Channel attribute from within a Credential attribute to optimize
scans. However, this design is not actually used with the WPS NFC use
cases. With configuration token, the AP Channel attribute is in the same
container with the Credential attribute (and that was also handled in
the previous implementation). With connection handover, AP Channel
information is outside the Credential attribute as well.

Simplify implementation by removing the AP Channel within Credential
case. This allows wpas_wps_use_cred() to get the AP Channel from the
container instead of having to find this during credential iteration.

Signed-hostap: Jouni Malinen <jouni@qca.qualcomm.com>