Remove lastSuccessfulCheck error

In GitHub Desktop Plus, we disabled automatic updates and rely on package managers instead. This error doesn't make sense anymore.

Author: pol-rivero

app/src/ui/about/about.tsx

@@ -190,16 +190,6 @@ export class About extends React.Component<IAboutProps> {
       )
     }
 
-    if (!this.props.updateState.lastSuccessfulCheck) {
-      return (
-        <DialogError>
-          Couldn't determine the last time an update check was performed. You
-          may be running an old version. Please try manually checking for
-          updates and contact GitHub Support if the problem persists
-        </DialogError>
-      )
-    }
-
     return null
   }