Revert "[NFC] Move DroppedVariableStats to its own file and redesign it to be extensible. (#115563)"
This reverts commit 2de78815604e9027efd93cac27c517bf732587d2.
Reverted due to buildbot failure:
unittests/IR/CMakeFiles/IRTests.dir/DroppedVariableStatsIRTest.cpp.o:DroppedVariableStatsIRTest.cpp:function llvm::DroppedVariableStatsIR::runAfterPass(llvm::StringRef, llvm::Any): error: undefined reference to 'llvm::DroppedVariableStatsIR::runOnModule(llvm::Module const*, bool)'