Wifi: Replace dual_band with 5GHz band support

As part of the support of the 6GHz band, the concept of dual-band is no
longer valid since we have more than 2 bands supported by Android and
can be checked on the device.
This commit replaces checks on dual-band support with an explicit check
on 5GHz band support.
This commit also removes the feature flags of 5GHz/6GHz support, since
these capabilities will be read from the overlay configs.

Bug: 145936758
Bug: 139354972
Test: Manual
Change-Id: I223ed2bc88c01f561d31abce4e2c91aa62da186f
Merged-In: I223ed2bc88c01f561d31abce4e2c91aa62da186f