[RISCV] Remove unnecessary check for RVE from determineCalleeSaves. NFCI

The SavedRegs BitVector is checks against the CSR list later. We have
a separate CSR list for RVE that excludes X16-31 so we don't need
to filter here.

If it was needed, it would be needed for the next block of code too
which didn't have an RVE check.

Author: topperc

llvm/lib/Target/RISCV/RISCVFrameLowering.cpp

@@ -1003,9 +1003,7 @@ void RISCVFrameLowering::determineCalleeSaves(MachineFunction &MF,
     };
 
     for (auto Reg : CSRegs)
-      // Only save x0-x15 for RVE.
-      if (Reg < RISCV::X16 || !Subtarget.isRVE())
-        SavedRegs.set(Reg);
+      SavedRegs.set(Reg);
 
     // According to psABI, if ilp32e/lp64e ABIs are used with an ISA that
     // has any of the registers x16-x31 and f0-f31, then these registers are