removed duplicate class (#2673)

Author: Pranav-Kunjir

docs/getting-started/quickstart.chrome-extension.mdx

@@ -133,7 +133,7 @@ sdk: chrome-extension
   function IndexPopup() {
     return (
       <ClerkProvider publishableKey={PUBLISHABLE_KEY}>
-        <div className="plasmo-flex plasmo-items-center plasmo-justify-center plasmo-h-[600px] plasmo-w-[800px] plasmo-flex plasmo-flex-col">
+        <div className="plasmo-flex plasmo-items-center plasmo-justify-center plasmo-h-[600px] plasmo-w-[800px] plasmo-flex-col">
           <header className="plasmo-w-full">
             <SignedOut>
               <SignInButton mode="modal" />