Remove some imports of model.dart (#2809)

Author: jcollins-g

lib/src/model/comment_referable.dart

@@ -11,7 +11,11 @@ import 'dart:core';
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/scope.dart';
-import 'package:dartdoc/src/model/model.dart';
+import 'package:dartdoc/src/model/accessor.dart';
+import 'package:dartdoc/src/model/container.dart';
+import 'package:dartdoc/src/model/library.dart';
+import 'package:dartdoc/src/model/model_element.dart';
+import 'package:dartdoc/src/model/nameable.dart';
 import 'package:dartdoc/src/model/package_graph.dart';
 import 'package:meta/meta.dart';
 

test/end2end/dartdoc_test.dart

@@ -15,7 +15,9 @@ import 'package:dartdoc/src/failure.dart';
 import 'package:dartdoc/src/generator/generator.dart';
 import 'package:dartdoc/src/io_utils.dart';
 import 'package:dartdoc/src/logging.dart';
-import 'package:dartdoc/src/model/model.dart';
+import 'package:dartdoc/src/model/class.dart';
+import 'package:dartdoc/src/model/documentable.dart';
+import 'package:dartdoc/src/model/model_element.dart';
 import 'package:dartdoc/src/model/package_builder.dart';
 import 'package:dartdoc/src/model/package_graph.dart';
 import 'package:dartdoc/src/package_config_provider.dart';