[LV] Unconditionally run materializeConstVTC in ::executePlan (#191299)
After https://github.com/llvm/llvm-project/pull/189372 both minimum
iteration checks for epilogue vectorization are created in VPlan, which
removes the last blocker for unconditionally running
materializeConstantVectorTripCount. This enables additional folds for
plans in the native path, as well as removes some trip count
computations with epilogue vectorization.
PR: https://github.com/llvm/llvm-project/pull/191299