Delete analyzer plugin to avoid warnings

The plugin is not working at the moment, so there's no point in having
the entrypoint around either.

drift/tools/analyzer_plugin/bin/plugin.dart

@@ -1,38 +0,0 @@
-import 'dart:convert';
-import 'dart:isolate';
-
-import 'package:drift_dev/integrations/plugin.dart' as plugin;
-import 'package:web_socket_channel/io.dart';
-
-const useDebuggingVariant = false;
-
-void main(List<String> args, SendPort sendPort) {
-  if (useDebuggingVariant) {
-    _PluginProxy(sendPort).start();
-  } else {
-    plugin.start(args, sendPort);
-  }
-}
-
-// Used during development. See CONTRIBUTING.md in the drift repo on how to
-// debug the plugin.
-class _PluginProxy {
-  final SendPort sendToAnalysisServer;
-
-  _PluginProxy(this.sendToAnalysisServer);
-
-  Future<void> start() async {
-    final channel = IOWebSocketChannel.connect('ws://localhost:9999');
-    final receive = ReceivePort();
-    sendToAnalysisServer.send(receive.sendPort);
-
-    receive.listen((data) {
-      // the server will send messages as maps, convert to json
-      channel.sink.add(json.encode(data));
-    });
-
-    channel.stream.listen((data) {
-      sendToAnalysisServer.send(json.decode(data as String));
-    });
-  }
-}

drift/tools/analyzer_plugin/pubspec.yaml

@@ -1,18 +0,0 @@
-name: analyzer_load_drift_plugin
-version: 1.0.0
-description: This pubspec is a part of Drift and determines the version of the analyzer plugin to load
-
-environment:
-  sdk: '>=2.17.0 <3.0.0'
-
-dependencies:
-  drift_dev: ^2.0.0
-  web_socket_channel: ^2.2.0
-
-# These overrides are only needed when working on the plugin with useDebuggingVariant = false (not recommended)
-
-#dependency_overrides:
-# drift_dev:
-#  path: /path/to/drift/drift_dev
-# sqlparser:
-#  path: /path/to/drift/sqlparser