[X86] Remove old instruction itinerary classes

[RKSimon]

Bugzilla Link	37093
Resolution	FIXED
Resolved on	Apr 13, 2018 08:58
Version	trunk
OS	Windows NT
Depends On	#31778
Blocks	#31672
CC	@adibiagio,@legrosbuffle,@topperc

Extended Description

Now that D45486 has landed (rL32983r/rL329837), we have no reason to keep the x86 instruction itineraries

[RKSimon]

assigned to @RKSimon

[RKSimon]

All instruction itineraries are now removed from trunk