Remove ISA from boot image name.

Partially reverts b9beb2e2efb6a204a69ca660d478b45f851e8f09

Bug: 14882223

(cherry picked from commit 3da44327c8306bb354c0163a7c7779dea6eeb38a)

Change-Id: Idc9266a97d1047434c110ef140e2f2708c4aadef
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index 7d7024a..ad796f8 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -958,9 +958,7 @@
   bool image = (!image_filename.empty());
   if (!image && boot_image_filename.empty()) {
     boot_image_filename += GetAndroidRoot();
-    boot_image_filename += "/framework/boot-";
-    boot_image_filename += GetInstructionSetString(instruction_set);
-    boot_image_filename += ".art";
+    boot_image_filename += "/framework/boot.art";
   }
   std::string boot_image_option;
   if (!boot_image_filename.empty()) {