Remove code supporting incremental compilation in dart2js

pkg/compiler/lib/src/use_unused_api.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// This file use methods that aren't used by dart2js.dart, but that we wish to
 /// keep anyway. This might be general API that isn't currently in use,
 /// debugging aids, or API only used for testing (see TODO below).
 
 library dart2js.use_unused_api;
 
@@ skipping 52 matching lines @@
   useJsOther(new js.SimpleJavaScriptPrintingContext());
   useJsBackend(null);
   useColor();
   useFilenames();
   useSsa(null);
   useIo();
   usedByTests();
   useElements();
   useCompiler(null);
   useTypes();
-  useCodeEmitterTask(null);
   useScript(null);
-  useProgramBuilder(null);
   useSemanticVisitor();
   useDeferred();
 }
 
 useApi([api.ReadStringFromUri uri, compiler.Compiler compiler]) {
   compiler.analyzeUri(null);
   new diagnostics.SourceSpan.fromNode(null, null);
 }
 
 class NullConstantConstructorVisitor
@@ skipping 190 matching lines @@
   pce.copyWithEnclosing(null);
   pfe.copyWithEnclosing(null);
   l.forEachImport(null);
 }
 
 useCompiler(compiler.Compiler c) {
   c.libraryLoader
     ..reset()
     ..resetAsync(null)
     ..lookupLibrary(null);
-  c.forgetElement(null);
   c.backend.constantCompilerTask.copyConstantValues(null);
   c.currentlyInUserCode();
 }
 
 useTypes() {}
 
-useCodeEmitterTask(js_emitter.CodeEmitterTask codeEmitterTask) {
-  full.Emitter fullEmitter = codeEmitterTask.emitter;
-  fullEmitter.clearCspPrecompiledNodes();
-  fullEmitter.buildLazilyInitializedStaticField(null, isolateProperties: null);
-}
-
 useScript(Script script) {
   script.copyWithFile(null);
 }
 
-useProgramBuilder(program_builder.ProgramBuilder builder) {
-  builder.buildMethodHackForIncrementalCompilation(null);
-  builder.buildFieldsHackForIncrementalCompilation(null);
-}
-
 useSemanticVisitor() {
   operators.UnaryOperator.fromKind(null);
   operators.BinaryOperator.fromKind(null);
   new semantic_visitor.BulkSendVisitor()..apply(null, null);
   new semantic_visitor.TraversalVisitor(null).apply(null, null);
   new semantic_visitor.BulkDeclarationVisitor().apply(null, null);
 }
 
 useDeferred([deferred.DeferredLoadTask task]) {
   task.dump();
 }