Remove old-skool font-support since woff and woff2 would be sufficient for our browser support

wagtail/admin/static_src/wagtailadmin/scss/_font-icons.scss

@@ -1,19 +1,7 @@
 // The wagtail font isn't available in WOFF2, so a @font-face is set here without a mixin.
 @font-face {
     font-family: 'wagtail';
-    src: url('#{$font-root}wagtail.eot');
-    src: url('#{$font-root}wagtail.eot?#iefix') format('embedded-opentype'),
-        url('#{$font-root}wagtail.ttf') format('truetype'),
-        url('#{$font-root}wagtail.svg#wagtail') format('svg'),
-        url('#{$font-root}wagtail.woff') format('woff');
+    src: url('#{$font-root}wagtail.woff') format('woff');
     font-weight: normal;
     font-style: normal;
 }
-
-// One exception to the limited font formats used above is the Wagtail icon font for Windows, where using the SVG version improves antialiasing
-@media screen and (-webkit-min-device-pixel-ratio: 0) {
-    @font-face {
-        font-family: 'wagtail';
-        src: url('#{$font-root}wagtail.svg#wagtail') format('svg');
-    }
-}

wagtail/admin/static_src/wagtailadmin/scss/_fonts.scss

@@ -1,15 +1,13 @@
 //  NB: Due to Wagtail's browser support the following @font-face formats are required:
 //  - WOFF for modern browsers
 //  - WOFF2 For super-modern browsers
-//  - TTF for older Android & iOS
 //
 //  This example is all we need now:
 //
 //  @font-face {
 //    font-family: 'MyWebFont';
 //    src: url('myfont.woff2') format('woff2'),
-//         url('myfont.woff') format('woff'),
-//         url('myfont.ttf') format('truetype');
+//         url('myfont.woff') format('woff');
 //  }
 //
 //  See https://css-tricks.com/snippets/css/using-font-face/ for more information.

wagtail/admin/static_src/wagtailadmin/scss/_mixins.scss

@@ -114,8 +114,7 @@
     @font-face {
         font-family: '#{$fontname}';
         src: url('#{$font-root}#{$filestub}.woff2') format('woff2'),
-            url('#{$font-root}#{$filestub}.woff') format('woff'),
-            url('#{$font-root}#{$filestub}.ttf') format('truetype');
+            url('#{$font-root}#{$filestub}.woff') format('woff');
         font-weight: $weight;
         font-style: $style;
     }