Revert "[BFI] Use CallbackVH to notify BFI about deletion of basic blocks"

This reverts commit 8975aa6e.

Causes a compilation warning:
llvm-project/llvm/include/llvm/Analysis/BlockFrequencyInfoImpl.h:1037:43: warning: 'llvm::BlockFrequencyInfoImpl<llvm::BasicBlock>::BFICallbackVH' has virtual functions but non-virtual destructor [-Wnon-virtual-dtor]
class BlockFrequencyInfoImpl<BasicBlock>::BFICallbackVH : public CallbackVH {
                                          ^
1 warning generated.