[RISCV] Remove redundant dependency on SlotIndexes in RISCVInsertVSETVLI. NFC

SlotIndexes is already marked as a transitive requirement of
LiveIntervals, so we don't need to specify it again in
RISCVInsertVSETVLI.

Author: lukel97

llvm/lib/Target/RISCV/RISCVInsertVSETVLI.cpp

@@ -892,7 +892,6 @@ class RISCVInsertVSETVLI : public MachineFunctionPass {
 
     AU.addUsedIfAvailable<LiveIntervals>();
     AU.addPreserved<LiveIntervals>();
-    AU.addUsedIfAvailable<SlotIndexes>();
     AU.addPreserved<SlotIndexes>();
     AU.addPreserved<LiveDebugVariables>();
     AU.addPreserved<LiveStacks>();