Fix even more analyser hints

Author: samogot

build_runner/lib/src/server/server.dart

@@ -23,7 +23,6 @@ const _performancePath = r'$perf';
 final _graphPath = r'$graph';
 final _assetsDigestPath = r'$assetDigests';
 final _buildUpdatesProtocol = r'$livereload';
-final _buildUpdatesMessage = 'update';
 final entrypointExtensionMarker = '/* ENTRYPOINT_EXTENTION_MARKER */';
 
 final _logger = Logger('Serve');
@@ -158,7 +157,7 @@ class BuildUpdatesWebSocketHandler {
   final WatchImpl _state;
 
   BuildUpdatesWebSocketHandler(this._state,
-      [this._handlerFactory = webSocketHandler]) {}
+      [this._handlerFactory = webSocketHandler]);
 
   shelf.Handler createHandlerByRootDir(String rootDir) {
     if (!_internalHandlers.containsKey(rootDir)) {