Revert 85678/85680. The decision is to stay with the current form of

Revert 85678/85680.  The decision is to stay with the current form of
indirectbr, thus we don't need "blockaddr(@func, null)".  Eliminate it
for simplicity.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@85699 91177308-0d34-0410-b5e6-96231b3b80d8