Remove LLVMGetTargetMachineData in go-binding.

Summary:
LLVMGetTargetMachineData has been removed, and LLVMGetDataLayout is
suggested to use. The LLVMGetDataLayout is exposed in go bindings.
So it's safe to remove the function.

Reviewers: bkramer

Subscribers: llvm-commits, axw

Differential Revision: http://reviews.llvm.org/D17193

llvm-svn: 260670