[GlobalOpt] Fix assertion failure during instruction deletion

This fixes the assertion failure reported in https://reviews.llvm.org/D114889#3166417,
by making RecursivelyDeleteTriviallyDeadInstructionsPermissive()
more permissive. As the function accepts a WeakTrackingVH, even if
originally only Instructions were inserted, we may end up with
different Value types after a RAUW operation. As such, we should
not assume that the vector only contains instructions.

Notably this matches the behavior of the
RecursivelyDeleteTriviallyDeadInstructions() function variant which
accepts a single value rather than vector.