[LV] Clean up unused 'using' definition (NFC) (#130597)

Author: artagnon

llvm/lib/Transforms/Vectorize/LoopVectorize.cpp

@@ -968,8 +968,6 @@ enum ScalarEpilogueLowering {
   CM_ScalarEpilogueNotAllowedUsePredicate
 };
 
-using InstructionVFPair = std::pair<Instruction *, ElementCount>;
-
 /// LoopVectorizationCostModel - estimates the expected speedups due to
 /// vectorization.
 /// In many cases vectorization is not profitable. This can happen because of