generate_opcode.py has quickly grown into generating much more than just
opcode definitions, and now handles a few duplicate impls across the
different decode modes as well. some of the added impl generation
conflicts with still-existing hand-written impls from yore, so they
needed a bit of removing.
next will be the addition of a generic module for "probably what you
want" disassembly of x86, avoiding the 64-/32-/16-bitness of the
architecture family with an attempt to decode "probably what you wanted"
from a byte sequence. it needs a little more work still, but TODO stubs
added here support that new module.