Cleanup flutter config output (#122384)

packages/flutter_tools/lib/src/features.dart

@@ -239,21 +239,17 @@ class Feature {
     if (configSetting == null) {
       return null;
     }
-    final StringBuffer buffer = StringBuffer('Enable or disable $name. '
-        'This setting will take effect on ');
+    final StringBuffer buffer = StringBuffer('Enable or disable $name.');
     final List<String> channels = <String>[
       if (master.available) 'master',
       if (beta.available) 'beta',
       if (stable.available) 'stable',
     ];
+    // Add channel info for settings only on some channels.
     if (channels.length == 1) {
-      buffer.write('the ${channels.single} channel.');
+      buffer.write('\nThis setting applies to only the ${channels.single} channel.');
     } else if (channels.length == 2) {
-      buffer.write('the ${channels.join(' and ')} channels.');
-    } else {
-      final String prefix = (channels.toList()
-        ..removeLast()).join(', ');
-      buffer.write('the $prefix, and ${channels.last} channels.');
+      buffer.write('\nThis setting applies to only the ${channels.join(' and ')} channels.');
     }
     if (extraHelpText != null) {
       buffer.write(' $extraHelpText');

packages/flutter_tools/test/general.shard/features_test.dart

@@ -89,26 +89,22 @@ void main() {
 
     testWithoutContext('Flutter web help string', () {
       expect(flutterWebFeature.generateHelpMessage(),
-      'Enable or disable Flutter for web. '
-      'This setting will take effect on the master, beta, and stable channels.');
+      'Enable or disable Flutter for web.');
     });
 
     testWithoutContext('Flutter macOS desktop help string', () {
       expect(flutterMacOSDesktopFeature.generateHelpMessage(),
-      'Enable or disable support for desktop on macOS. '
-      'This setting will take effect on the master, beta, and stable channels.');
+      'Enable or disable support for desktop on macOS.');
     });
 
     testWithoutContext('Flutter Linux desktop help string', () {
       expect(flutterLinuxDesktopFeature.generateHelpMessage(),
-      'Enable or disable support for desktop on Linux. '
-      'This setting will take effect on the master, beta, and stable channels.');
+      'Enable or disable support for desktop on Linux.');
     });
 
     testWithoutContext('Flutter Windows desktop help string', () {
       expect(flutterWindowsDesktopFeature.generateHelpMessage(),
-      'Enable or disable support for desktop on Windows. '
-      'This setting will take effect on the master, beta, and stable channels.');
+      'Enable or disable support for desktop on Windows.');
     });
 
     testWithoutContext('help string on multiple channels', () {
@@ -120,8 +116,7 @@ void main() {
         configSetting: 'foo',
       );
 
-      expect(testWithoutContextFeature.generateHelpMessage(), 'Enable or disable example. '
-          'This setting will take effect on the master, beta, and stable channels.');
+      expect(testWithoutContextFeature.generateHelpMessage(), 'Enable or disable example.');
     });
 
     /// Flutter Web