Remove outdated TODO on Return in LIR generator

Summary:
There's nothing stopping us from passing a constant value to the LIR Return
instruction here anymore.  It's already handled in regalloc.

Reviewed By: brittanyrey

Differential Revision: D55969686

fbshipit-source-id: 49f44a52578b369af65065eb25adbf213b724a13

cinderx/Jit/lir/generator.cpp

@@ -1095,7 +1095,6 @@ LIRGenerator::TranslatedBlock LIRGenerator::TranslateOneBasicBlock(
         break;
       }
       case Opcode::kReturn: {
-        // TODO support constant operand to Return
         bbb.appendInstr(Instruction::kReturn, i.GetOperand(0));
         break;
       }