Remove SRI of bootstrap and font-awesome css

Sometimes it causes the fetch event to fail after the PWA cache key is updated:

```
The FetchEvent for "<url_from_CDN>" resulted in a network error response: an "opaque" response was used for a request whose type is not no-cors
```

Author: cotes2020

_includes/head.html

@@ -55,15 +55,10 @@
   <link rel="dns-prefetch" href="https://cdn.jsdelivr.net">
 
   <!-- Bootstrap -->
-  <link rel="stylesheet"
-    href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css"
-    integrity="sha256-LA89z+k9fjgMKQ/kq4OO2Mrf8VltYml/VES+Rg0fh20=" crossorigin="anonymous">
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/[email protected]/dist/css/bootstrap.min.css">
 
   <!-- Font Awesome -->
-  <link rel="stylesheet"
-    href="https://cdn.jsdelivr.net/npm/@fortawesome/[email protected]/css/all.min.css"
-    integrity="sha256-+N4/V/SbAFiW1MPBCXnfnP9QSN3+Keu+NlB+0ev/YKQ="
-    crossorigin="anonymous">
+  <link rel="stylesheet" href="https://cdn.jsdelivr.net/npm/@fortawesome/[email protected]/css/all.min.css">
 
   {% include css-selector.html %}