Update CSP to remove incorrect usages.

public/_headers

@@ -1,7 +1,7 @@
 https://www.waterfox.net/*
 Access-Control-Allow-Origin: https://www.waterfox.net
 Cache-Control: no-store, max-age=0
-Content-Security-Policy: block-all-mixed-content; upgrade-insecure-requests; require-trusted-types-for 'script'
+Content-Security-Policy: upgrade-insecure-requests
 Cross-Origin-Embedder-Policy: require-corp
 Cross-Origin-Opener-Policy: same-origin
 Cross-Origin-Resource-Policy: same-origin