Remove spinjs-rails dependency and use spinning-circles.svg instead.

For https://github.com/openfoodfoundation/openfoodnetwork/issues/3491

The spinjs-rails gem provides a CSS3 a spinning activity indicator. This commit removes the gem so we don't have to keep the gem up-to-date and uses the spinning-circles.svg which is used already in other places.

The spinjs spinner can be seen when viewing or editing taxonomies in /admin/taxonomies. It is loaded from the .ajaxStart call in app/assets/javascripts/admin/spree/progress.coffee

To test or restyle this spinner you can change the display property of the #progress element in app/assets/stylesheets/admin/components/progress.scss to 'block'.

app/assets/javascripts/admin/all.js

@@ -30,7 +30,6 @@
 //= require spree
 //= require admin/spree/spree-select2
 //= require modernizr
-//= require spin
 //= require equalize
 //= require css_browser_selector_dev
 //= require responsive-tables

app/assets/javascripts/admin/spree/progress.coffee

@@ -1,27 +1,7 @@
 $(document).ready ->
-  opts =
-    lines: 11
-    length: 2
-    width: 3
-    radius: 9
-    corners: 1
-    rotate: 0
-    color: '#fff'
-    speed: 0.8
-    trail: 48
-    shadow: false
-    hwaccel: true
-    className: 'spinner'
-    zIndex: 2e9
-    top: 'auto'
-    left: 'auto'
-
-  target = document.getElementById("spinner")  
-
   $(document).ajaxStart ->
     $("#progress").fadeIn()
-    spinner = new Spinner(opts).spin(target)    
 
   $(document).ajaxStop ->
-    $("#progress").fadeOut()    
+    $("#progress").fadeOut()