Remove the port for rk30xx.
Kernel config was removed in r346096 and this port was never migrated
It is also impossible to obtain such hardware nowadays and this code
don't provide anything beside booting.
That was my first read, but I thought it useful to ask the bigger question which might be answered differently for other bits and to help establish norms here that are flexible for the obscure case, but useful when lots of people may be affected. Here the impact seems small enough