fix: remove the duplicate manifest tag (@malkiii) (monkeytypegame#6088)

!nuf

Author: malkiii

frontend/src/html/head.html

@@ -50,7 +50,6 @@
     content="/images/favicon/browserconfig.xml"
   />
   <meta id="metaThemeColor" name="theme-color" content="#e2b714" />
-  <link rel="manifest" href="/manifest.json" />
   <meta
     name="name"
     content="Monkeytype | A minimalistic, customizable typing test"