Remove Iceland.

ART_USE_LLVM_COMPILER is removed and when necessary ART_USE_PORTABLE_COMPILER
is used in #ifdefs.

Change-Id: Iffa9ce5b0246c7c427ccc4e67ecc134624632e55
diff --git a/src/compiler.h b/src/compiler.h
index 0f99f4d..9475642 100644
--- a/src/compiler.h
+++ b/src/compiler.h
@@ -42,8 +42,7 @@
 enum CompilerBackend {
   kQuick,
   kQuickGBC,
-  kPortable,
-  kIceland  // Temporary - remove soon
+  kPortable
 };
 
 // Thread-local storage compiler worker threads