[X86] Remove useless custom inserter for 64-bit TAILJMP and TCRETURN opcodes

This custom inserter was added in r124272 at which time it added about bunch of Defs for Win64. In r150708, those defs were removed leaving only the "return BB". So I think this means the custom inserter is a NOP these days.

This patch removes the remaining code and stops tagging the instructions for custom insertion

Differential Revision: https://reviews.llvm.org/D41671

llvm-svn: 321747