Revert "fixes #200, library prefixes for unknown imports"

This reverts commit 026a4921957ee08f011eabf1c3deea6c5e8aa715.

BUG=

Review URL: https://codereview.chromium.org/1159013009

Author: John Messerly

pkg/dev_compiler/lib/src/utils.dart

@@ -207,15 +207,8 @@ _MemberTypeGetter _memberTypeGetter(ExecutableElement member) {
   return f;
 }
 
-bool isDynamicTarget(Expression node) {
-  if (node == null) return false;
-  var type = node.staticType;
-
-  // This is an unknown identifier, like an import that doesn't resolve.
-  if (type == null) return true;
-
-  return type.isDynamic && !isLibraryPrefix(node);
-}
+bool isDynamicTarget(Expression node) =>
+    node != null && !isLibraryPrefix(node) && node.staticType.isDynamic;
 
 bool isLibraryPrefix(Expression node) =>
     node is SimpleIdentifier && node.staticElement is PrefixElement;