Remove support for Javascript warnings in the VM.

runtime/vm/stub_code_arm64.cc

Index: runtime/vm/stub_code_arm64.cc
diff --git a/runtime/vm/stub_code_arm64.cc b/runtime/vm/stub_code_arm64.cc
index 07b2b866c8b0249c9467684aeee28033cca80da2..ec83c5d9524608047ddb787abf4ff338ad10856f 100644
--- a/runtime/vm/stub_code_arm64.cc
+++ b/runtime/vm/stub_code_arm64.cc
@@ -1293,10 +1293,6 @@ static void EmitFastSmiOp(Assembler* assembler,
                           Label* not_smi_or_overflow,
                           bool should_update_result_range) {
   __ Comment("Fast Smi op");
-  if (FLAG_throw_on_javascript_int_overflow) {
-    // The overflow check is more complex than implemented below.
-    return;
-  }
   __ ldr(R0, Address(SP, + 0 * kWordSize));  // Right.
   __ ldr(R1, Address(SP, + 1 * kWordSize));  // Left.
   __ orr(TMP, R0, Operand(R1));