Remove dead code for parsing/emitting X86 instructions

[filipnavara]

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[huoyaoyuan]

There are a bit more dead patterns: #103533 (comment)

A little portion of dead code accessing ESP+offset is not removed in stublinkerx86.

Can we figure out what are alive now?

[filipnavara]

I removed bulk of the code in #115339 and now I checked every remaining method if it's used or not.

[filipnavara]

On second look I found more things to remove. We can likely remove the single usage of X86EmitNearJump too and that will make another big chunk go away.

[jkotas]

Thanks!