Remove .eot & .ttf fonts

No issue

According to [caniuse](http://caniuse.com/#feat=woff), all the browsers we support (last 2 versions of major browsers) support the `.woff` font format. It's actually what pretty much all browsers will serve if its offered anyway.

This PR removes the .eot and .ttf font formats.

SVG remains as its the base file we use to add new icons & convert into other formats. It is not referenced anywhere.

core/client/assets/sass/modules/icons.scss

@@ -25,11 +25,7 @@
 
 @font-face {
     font-family: 'GhostIcons';
-    src:url('../fonts/icons.eot');
-    src:url('../fonts/icons.eot?#iefix') format('embedded-opentype'),
-        url('../fonts/icons.woff') format('woff'),
-        url('../fonts/icons.ttf') format('truetype'),
-        url('../fonts/icons.svg#icons') format('svg');
+    src:url('../fonts/icons.woff') format('woff');
     font-weight: normal;
     font-style: normal;
 }