Remove type conversion nodes converting to the same type.

When optimizing, we ensure these conversions do not reach the
code generators. When not optimizing, we cannot get such situations.

Change-Id: I717247c957667675dc261183019c88efa3a38452
diff --git a/compiler/optimizing/code_generator_arm64.cc b/compiler/optimizing/code_generator_arm64.cc
index 943f71f..a61ef2d 100644
--- a/compiler/optimizing/code_generator_arm64.cc
+++ b/compiler/optimizing/code_generator_arm64.cc
@@ -2129,6 +2129,7 @@
       new (GetGraph()->GetArena()) LocationSummary(conversion, LocationSummary::kNoCall);
   Primitive::Type input_type = conversion->GetInputType();
   Primitive::Type result_type = conversion->GetResultType();
+  DCHECK_NE(input_type, result_type);
   if ((input_type == Primitive::kPrimNot) || (input_type == Primitive::kPrimVoid) ||
       (result_type == Primitive::kPrimNot) || (result_type == Primitive::kPrimVoid)) {
     LOG(FATAL) << "Unexpected type conversion from " << input_type << " to " << result_type;