Remove duplicate logic in KeywordHelper

Change-Id: I32e7643f785228b99961e50bc2380bdcdffca1d2
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/430881
Commit-Queue: Keerti Parthasarathy <keertip@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

Author: keertip

pkg/analysis_server/lib/src/services/completion/dart/keyword_helper.dart

@@ -585,13 +585,6 @@ class KeywordHelper {
   /// beginning of a statement. The [node] provides context to determine which
   /// keywords to include.
   void addStatementKeywords(AstNode node) {
-    if (node.inAsyncMethodOrFunction) {
-      addKeyword(Keyword.AWAIT);
-    } else if (node.inAsyncStarOrSyncStarMethodOrFunction) {
-      addKeyword(Keyword.AWAIT);
-      addKeyword(Keyword.YIELD);
-      addKeywordAndText(Keyword.YIELD, '*');
-    }
     if (node.inLoop) {
       addKeyword(Keyword.BREAK);
       addKeyword(Keyword.CONTINUE);