fetch1/icache1: Remove the use_previous logic

fetch1/icache1: Remove the use_previous logic

This removes logic that I added some time ago with the thought that it
would enable us to do prefetching in the icache.  This logic detects
when the fetch address is an odd multiple of 4 and the next address in
sequence from the previous cycle.  In that case the instruction we
want is in the output register of the icache RAM already so there is
no need to do another read or any icache tag or TLB lookup.

However, this logic adds complexity, and removing it improves timing,
so this removes it.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>