Rename kDummy32BitOffset to kPlaceholder32BitOffset.

And drop an obsolete reference to Quick compiler.

Test: m test-art-host-gtest
Bug: 161336379
Change-Id: If08cc0ca83cfeb1c6923c41f9d61766f878a295a
diff --git a/compiler/optimizing/code_generator_x86.h b/compiler/optimizing/code_generator_x86.h
index c267f76..d2f1e77 100644
--- a/compiler/optimizing/code_generator_x86.h
+++ b/compiler/optimizing/code_generator_x86.h
@@ -657,9 +657,9 @@
   void MaybeGenerateInlineCacheCheck(HInstruction* instruction, Register klass);
   void MaybeIncrementHotness(bool is_frame_entry);
 
-  // When we don't know the proper offset for the value, we use kDummy32BitOffset.
+  // When we don't know the proper offset for the value, we use kPlaceholder32BitOffset.
   // The correct value will be inserted when processing Assembler fixups.
-  static constexpr int32_t kDummy32BitOffset = 256;
+  static constexpr int32_t kPlaceholder32BitOffset = 256;
 
  private:
   struct X86PcRelativePatchInfo : PatchInfo<Label> {