Remove 2023 deprecated 'platforms' key from daemon output (flutter#172593)

Closes flutter#140473.

Author: matanlurey

packages/flutter_tools/lib/src/commands/daemon.dart

@@ -599,11 +599,7 @@ class DaemonDomain extends Domain {
 
       PlatformType.values.forEach(handlePlatformType);
 
-      return <String, Object>{
-        // TODO(fujino): delete this key https://github.com/flutter/flutter/issues/140473
-        'platforms': platformTypes,
-        'platformTypes': platformTypesMap,
-      };
+      return <String, Object>{'platformTypes': platformTypesMap};
     } on Exception catch (err, stackTrace) {
       sendEvent('log', <String, Object?>{
         'log': 'Failed to parse project metadata',
@@ -613,7 +609,6 @@ class DaemonDomain extends Domain {
       // On any sort of failure, fall back to Android and iOS for backwards
       // compatibility.
       return const <String, Object>{
-        'platforms': <String>['android', 'ios'],
         'platformTypes': <String, Object>{
           'android': <String, Object>{'isSupported': true},
           'ios': <String, Object>{'isSupported': true},

packages/flutter_tools/test/commands.shard/hermetic/daemon_test.dart

@@ -124,7 +124,6 @@ void main() {
         expect(response.data['id'], 0);
         expect(response.data['result'], isNotEmpty);
         expect(response.data['result']! as Map<String, Object?>, const <String, Object>{
-          'platforms': <String>['macos', 'windows'],
           'platformTypes': <String, Map<String, Object>>{
             'web': <String, Object>{
               'isSupported': false,