display only 1 <MissingAnnotationEmptyState />

Per code review feedback, it's arguably unnecessary
to display duplicate `<MissingAnnotationEmptyState />`,
especially given the preceding contextual sentence
noting the supported annotations.

Signed-off-by: Mike Ball <mikedball@gmail.com>

plugins/splunk-on-call/src/components/EntitySplunkOnCallCard.tsx

@@ -55,7 +55,6 @@ export const MissingAnnotation = () => (
       <code>{SPLUNK_ON_CALL_ROUTING_KEY}</code> annotation.
     </Typography>
     <MissingAnnotationEmptyState annotation={SPLUNK_ON_CALL_TEAM} />
-    <MissingAnnotationEmptyState annotation={SPLUNK_ON_CALL_ROUTING_KEY} />
   </div>
 );