* decode.scm (-distinguishing-bit-population): Compute num-insns, the
number of insns in the list. Update the population count function to
identify and prioritize 3 catgories of useful bits.
(-population-top-few): Don't consider bits with a population count of
zero.
(-build-decode-table-entry): Don't call
filter-harmlessly-ambiguous-insns. Filter out non-specialized and
identical insns at the next tree level.
* insn.scm (filter-harmlessly-ambiguous-insns): Note in a comment that
this function is no longer used.
(filter-non-specialized-ambiguous-insns): New function.
(filter-identical-ambiguous-insns): New function.
(find-identical-insn): New function.
(filter-harmlessly-ambiguous-insns): Removed.