Remove the flawed, unused attempt to manually emulate Gecko codes.

Parsing Gecko codes (in any manner) is much like parsing HTML with regex
- that w̷a̶y̸ l̵i̷e̴s̵ m̴̲a̵͈d̵̝n̵̙ę̵͎̞̼̙̼͔̞͖͎̝s̵̨̬̱͍͓͉̠̯̤͙̝s̷͍̲̲̭̼͍͎͖̤̭̘.  Luckily, with the embedded codehandler.bin,
the monstrosity may remain at only one implementation.  Anyway, removing
the inserted_asm_codes thing probably speeds up the interpreter a bit.
Add a non-tiny warning about CPUs that will silently desync.
Revert "Jit64: use AVX instructions in some places"

and the fixes afterwards

This reverts commit ff917897731d400a8e71c1480425733e651126ee.
This reverts commit bcefa880e4d062121df9ab8b831170ec3a689a50.
This reverts commit 710a0ff435c8593914c6eb074b6bc4d1985ae8c5.
This reverts commit ddaf29e039d1736be1ca48c1c0b6af1c8d4ec47d.
Jit64: load second operator for double intrutions

SSE do support non-vector instructions, but they _all_ overwrite the dest register
if the src location isn't a register. (wtf?)
So we have to load the src into a temporay register :(
Merge branch 'revert-avx'