Fixed #36: removed reference to SVG favicon

We've switched to light-theme only, PNG in 34fb98e in a multi-repo
effort. imager-service only writes PNG square and horizontal images
and offspot-config mounts the /branding/ folder (on purpose).

Keeping SVG and PNG is thus doomed to fail.

Author: rgaudin

branding/horizontal-logo.svg

@@ -4,7 +4,6 @@
     <meta charset="utf-8">
     <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=no" />
     <title>{{ name }}</title>
-    <link rel="icon" type="image/svg+xml" href="/branding/square-logo.svg">
     <link rel="icon" type="image/png" href="/branding/square-logo-light.png" media="(prefers-color-scheme:no-preference)">
     <link rel="icon" type="image/png" href="/branding/square-logo-dark.png"  media="(prefers-color-scheme:dark)">
     <link rel="icon" type="image/png" href="/branding/square-logo-light.png" media="(prefers-color-scheme:light)">