Remove __consuming from CodeCompletion

Set the UserInaccessible bit to remove __consuming from code
completion until we commit to a real keyword.

rdar://40828289

lib/IDE/CodeCompletion.cpp

@@ -4845,6 +4845,11 @@ static void addDeclKeywords(CodeCompletionResultSink &Sink) {
       // Treat keywords that could be the start of a pattern specially.
       return;
     }
+    // FIXME: __consuming should not appear in CodeCompletion until it is
+    // finalized in a language proposal.
+    if (Name == "__consuming")
+      return;
+
     CodeCompletionResultBuilder Builder(
         Sink, CodeCompletionResult::ResultKind::Keyword,
         SemanticContextKind::None, {});