[DeadArgElim] Strip allocsize attributes when deleting an argument.

Since allocsize refers to the argument number it gets invalidated when
an argument is removed and the numbers shift.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@328481 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed