Remove kDex2OatHostKey from oat-header

The oat-header used to include the ISA of the dex2oat used to compile
the image. This made cross-compiling a bitwise identical oat/image
file impossible and is not terribly useful so it was removed.

Test: ./test.py --host
Bug: 119332327
Change-Id: If9d21b5997907ee01283d1345749a01e2a2359ea
diff --git a/dex2oat/dex2oat.cc b/dex2oat/dex2oat.cc
index d901c01..77928d3 100644
--- a/dex2oat/dex2oat.cc
+++ b/dex2oat/dex2oat.cc
@@ -1055,9 +1055,6 @@
         oss << argv[i];
       }
       key_value_store_->Put(OatHeader::kDex2OatCmdLineKey, oss.str());
-      oss.str("");  // Reset.
-      oss << kRuntimeISA;
-      key_value_store_->Put(OatHeader::kDex2OatHostKey, oss.str());
     }
     key_value_store_->Put(
         OatHeader::kDebuggableKey,
diff --git a/runtime/oat.h b/runtime/oat.h
index b07294a..3d6415e 100644
--- a/runtime/oat.h
+++ b/runtime/oat.h
@@ -35,7 +35,6 @@
   static constexpr uint8_t kOatVersion[] = { '1', '6', '3', '\0' };
 
   static constexpr const char* kDex2OatCmdLineKey = "dex2oat-cmdline";
-  static constexpr const char* kDex2OatHostKey = "dex2oat-host";
   static constexpr const char* kDebuggableKey = "debuggable";
   static constexpr const char* kNativeDebuggableKey = "native-debuggable";
   static constexpr const char* kCompilerFilter = "compiler-filter";