Remove unused RADIUS client reconfig function

This is not actually used at all and it looks like the rules for
maintaining the old/new RADIUS configuration are not very clear in the
case the RADIUS client configuration did not change. Consequently, it
is better to just remove this for now and if similar functionality is
ever needed, redesign it to be easier to use without causing hard to
find issues with using freed memory.

Simpler approach to reconfiguring the RADIUS client would involve
just deinitializing the old context unconditionally and initializing
a new one whenever the configuration could have changed.