fix wizard opening every time on start even when completed

Summary:
1. When setup wizard was first launched some people may have manually added aother values in local storage that are not literal string "true". This may cause setup wizard to still open when flipper is relaunched. Now we check for any value. If the key is not set in localStorage. it will return `null`.
2. Actually only open setup wizard when it has **NOT** been completed 🤦

Reviewed By: mweststrate

Differential Revision: D52456307

fbshipit-source-id: 4fc070af27645661e43dbf664d7474c85d32a1e5

desktop/flipper-ui/src/chrome/FlipperSetupWizard.tsx

@@ -264,6 +264,6 @@ export function hasSetupWizardCompleted(
 ): boolean {
   return (
     !localStorage ||
-    localStorage.getItem(SETUP_WIZARD_FINISHED_LOCAL_STORAGE_KEY) !== 'true'
+    localStorage.getItem(SETUP_WIZARD_FINISHED_LOCAL_STORAGE_KEY) != null
   );
 }

desktop/flipper-ui/src/sandy-chrome/SandyApp.tsx

@@ -54,7 +54,7 @@ export function SandyApp() {
 
     uiPerfTracker.track('ui-perf-sandy-container-rendered');
 
-    if (hasSetupWizardCompleted(window.localStorage)) {
+    if (!hasSetupWizardCompleted(window.localStorage)) {
       Dialog.showModal((onHide) => (
         <FlipperSetupWizard onHide={onHide} closable={false} />
       ));