Bluetooth: host: Remove dependency on host emulation for debug ECC keys

Remove the depency on host emulation of ECC for the Use debug keys
option.
This allows the application to use debug keys without shifting the
ECC from the controller to the host, which could potentially alter
the behavior of the application and make debugging this way less useful.

Signed-off-by: Joakim Andersson <joakim.andersson@nordicsemi.no>