Remove an obsolete error from the spec and an obsolete command-line flag

pkg/analysis_server/lib/src/domain_completion.dart

Index: pkg/analysis_server/lib/src/domain_completion.dart
diff --git a/pkg/analysis_server/lib/src/domain_completion.dart b/pkg/analysis_server/lib/src/domain_completion.dart
index 77c3e86f4cd2b1b45ad1c7875b865c8cb40e4741..88d49580216b09b705a3acce74afe44bf3881f48 100644
--- a/pkg/analysis_server/lib/src/domain_completion.dart
+++ b/pkg/analysis_server/lib/src/domain_completion.dart
@@ -139,9 +139,6 @@ class CompletionDomainHandler extends AbstractRequestHandler {
 
   @override
   Response handleRequest(Request request) {
-    if (server.searchEngine == null) {
-      return new Response.noIndexGenerated(request);
-    }
     return runZoned(() {
       String requestName = request.method;
       if (requestName == COMPLETION_GET_SUGGESTIONS) {