[turbofan] remove checks for virtual register overflow

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index f83cdebede03e33e2e6badfdb0ebf147db91360e..0989019c0c67829ccff1f4240fee03d8147e3547 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -458,6 +458,13 @@ InstructionSequence::InstructionSequence(Zone* instruction_zone,
 }
 
 
+int InstructionSequence::NextVirtualRegister() {
+  int virtual_register = next_virtual_register_++;
+  CHECK_NE(virtual_register, UnallocatedOperand::kInvalidVirtualRegister);
+  return virtual_register;
+}
+
+
 BlockStartInstruction* InstructionSequence::GetBlockStart(
     BasicBlock::RpoNumber rpo) const {
   const InstructionBlock* block = InstructionBlockAt(rpo);