Remove "unnecessary" imports. (#75198)

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.

See https://github.com/dart-lang/sdk/issues/44569 for more information.

packages/flutter/test/painting/border_rtl_test.dart

@@ -7,7 +7,6 @@ import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';
-import '../rendering/rendering_tester.dart';
 
 class SillyBorder extends BoxBorder {
   @override

packages/flutter/test/painting/colors_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
-import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
 

packages/flutter/test/painting/common_matchers.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';

packages/flutter/test/painting/continuous_rectangle_border_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'package:flutter/material.dart';
-import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import '../rendering/mock_canvas.dart';

packages/flutter/test/painting/flutter_logo_test.dart

@@ -4,7 +4,6 @@
 
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:flutter/painting.dart';
 
 void main() {
   // Here and below, see: https://github.com/dart-lang/sdk/issues/26980

packages/flutter/test/painting/gradient_test.dart

@@ -6,7 +6,6 @@ import 'dart:math' as math;
 
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
-import 'package:flutter/painting.dart';
 
 void main() {
   test('LinearGradient scale test', () {

packages/flutter/test/painting/image_provider_network_image_test.dart

@@ -12,7 +12,6 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../flutter_test_alternative.dart' show Fake;
 import '../image_data.dart';
 import '../rendering/rendering_tester.dart';
 

packages/flutter/test/painting/image_test_utils.dart

@@ -8,8 +8,6 @@ import 'dart:ui' as ui;
 import 'package:flutter/foundation.dart';
 import 'package:flutter/painting.dart';
 
-import 'package:flutter_test/flutter_test.dart';
-
 class TestImageProvider extends ImageProvider<TestImageProvider> {
   TestImageProvider(this.testImage);
 

packages/flutter/test/painting/system_fonts_test.dart

@@ -3,9 +3,7 @@
 // found in the LICENSE file.
 
 import 'package:flutter/foundation.dart';
-import 'package:flutter/rendering.dart';
 import 'package:flutter/material.dart';
-import 'package:flutter/widgets.dart';
 import 'package:flutter/cupertino.dart';
 import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';

packages/flutter/test/painting/text_painter_test.dart

@@ -4,12 +4,9 @@
 
 import 'dart:ui' as ui;
 
-import 'package:flutter/painting.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
-import '../flutter_test_alternative.dart' show Fake;
-
 void main() {
   test('TextPainter caret test', () {
     final TextPainter painter = TextPainter()

packages/flutter/test/painting/text_span_test.dart

@@ -2,7 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-import 'package:flutter/painting.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';