[X86] Remove all the vector NOP bitcast patterns. Use a few lines of code in...

[X86] Remove all the vector NOP bitcast patterns. Use a few lines of code in the Select method in X86ISelDAGToDAG.cpp instead.

There are a lot of permutations of types here generating a lot of patterns in the isel table. It's more efficient to just ReplaceUses and RemoveDeadNode from the Select function.

The test changes are because we have a some shuffle patterns that have a bitcast as their root node. But the behavior is identical to another instruction whose pattern doesn't start with a bitcast. So this isn't a functional change.

llvm-svn: 338824