[MC] Remove dead code, NFC

This code was added in 408b5e6, but neither the return value nor
`Res` was used in the following code.

Differential Revision: https://reviews.llvm.org/D149584

Author: phoebewang

llvm/lib/MC/MCCodeView.cpp

@@ -649,8 +649,6 @@ void CodeViewContext::encodeDefRange(MCAsmLayout &Layout,
       const MCSymbolRefExpr *SRE = MCSymbolRefExpr::create(RangeBegin, Ctx);
       const MCBinaryExpr *BE =
           MCBinaryExpr::createAdd(SRE, MCConstantExpr::create(Bias, Ctx), Ctx);
-      MCValue Res;
-      BE->evaluateAsRelocatable(Res, &Layout, /*Fixup=*/nullptr);
 
       // Each record begins with a 2-byte number indicating how large the record
       // is.