Remove and also ignore unnecessary imports

In each library where an import is removed, the library uses some elements
provided by the import, BUT there is another import which provides all of the
same elements, and at least one more which the library uses.

In this change, we remove the imports which can be simply removed in favor of
the other already present imports.

Additionally, I add an ignore to analysis_options.yaml, so that
unnecessary_import can land in Dart. After it lands, we can clean up the
remaining cases in flutter.

See dart-lang/sdk#44569 for more information.

Author: srawlins

analysis_options.yaml

@@ -36,6 +36,9 @@ analyzer:
     # Stream and not importing dart:async
     # Please see https://github.com/flutter/flutter/pull/24528 for details.
     sdk_version_async_exported_from_core: ignore
+    # TODO(https://github.com/flutter/flutter/issues/74381):
+    # Clean up existing unnecessary imports, and remove line to ignore.
+    unnecessary_import: ignore
     # Turned off until null-safe rollout is complete.
     unnecessary_null_comparison: ignore
   exclude:

dev/integration_tests/deferred_components_test/lib/component1.dart

@@ -5,7 +5,6 @@
 library component1;
 
 import 'package:flutter/material.dart';
-import 'package:flutter/widgets.dart';
 
 
 class LogoScreen extends StatelessWidget {

dev/integration_tests/deferred_components_test/lib/main.dart

@@ -5,7 +5,6 @@
 import 'dart:async';
 
 import 'package:flutter/material.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter_driver/driver_extension.dart';
 
 import 'component1.dart' deferred as component1;

dev/tools/test/dartdoc_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'package:platform/platform.dart';
-import 'package:process/process.dart';
 import 'package:test/test.dart';
 
 import '../../../packages/flutter_tools/test/src/fake_process_manager.dart';