revert r158660, since Chris has some issues with this patch (namely using code to...

revert r158660, since Chris has some issues with this patch (namely using code to reprent information only used by the compiler)

Original commit msg:
add the 'alloc' metadata node to represent the size of offset of buffers pointed to by pointers.
This metadata can be attached to any instruction returning a pointer

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@158688 91177308-0d34-0410-b5e6-96231b3b80d8