FIX: Remove svg icons from webmanifest shortcuts (#15765)

* FIX: Remove svg icons from webmanifest shortcuts

While SVGs are valid in the webmanifest, Chromium has not implemented
support for it in this specific manifest member.

Revert when https://bugs.chromium.org/p/chromium/issues/detail?id=1091612
lands.

* fix test

spec/requests/metadata_controller_spec.rb

@@ -94,7 +94,7 @@ RSpec.describe MetadataController do
       expect(response.status).to eq(200)
       manifest = JSON.parse(response.body)
       expect(manifest["shortcuts"].size).to be > 0
-      expect { URI.parse(manifest["shortcuts"][0]["icons"][0]["src"]) }.not_to raise_error
+      expect { URI.parse(manifest["shortcuts"][0]["url"]) }.not_to raise_error
     end
   end