[RISCV] Remove -riscv-enable-vl-optimizer flag (#149349)

The RISCVVLOptimizer has been enabled by default for a while now and I'm
not aware of any outstanding issues that might need it to be disabled.
This removes the -riscv-enable-vl-optimizer flag to reduce the number of
configurations we have to support.

Author: lukel97

llvm/lib/Target/RISCV/RISCVTargetMachine.cpp

@@ -104,11 +104,6 @@ static cl::opt<bool> EnablePostMISchedLoadStoreClustering(
     cl::desc("Enable PostRA load and store clustering in the machine scheduler"),
     cl::init(true));
 
-static cl::opt<bool>
-    EnableVLOptimizer("riscv-enable-vl-optimizer",
-                      cl::desc("Enable the RISC-V VL Optimizer pass"),
-                      cl::init(true), cl::Hidden);
-
 static cl::opt<bool> DisableVectorMaskMutation(
     "riscv-disable-vector-mask-mutation",
     cl::desc("Disable the vector mask scheduling mutation"), cl::init(false),
@@ -617,8 +612,7 @@ void RISCVPassConfig::addPreRegAlloc() {
   addPass(createRISCVPreRAExpandPseudoPass());
   if (TM->getOptLevel() != CodeGenOptLevel::None) {
     addPass(createRISCVMergeBaseOffsetOptPass());
-    if (EnableVLOptimizer)
-      addPass(createRISCVVLOptimizerPass());
+    addPass(createRISCVVLOptimizerPass());
   }
 
   addPass(createRISCVInsertReadWriteCSRPass());