Remove vendor prefixed declarations

Since `gulp-autoprefixer` is part of the build process the
vendor prefixed declarations in the source Sass files are redundant

Author: jpersson

src/styles/core/_core.scss

@@ -103,8 +103,6 @@ button::-moz-focus-inner {
     box-shadow: 0 0 14px rgba(0,0,0,.24),
         0 14px 28px rgba(0,0,0,.48);
     transform: translateX(105%);
-    transition: -webkit-transform 0.233s cubic-bezier(0,0,0.21,1) 0.04s,
-      opacity 0.213s cubic-bezier(0,0,0.21,1) 0.04s;
     transition: transform 0.233s cubic-bezier(0,0,0.21,1) 0.04s,
       opacity 0.213s cubic-bezier(0,0,0.21,1) 0.04s;
     will-change: transform;

src/styles/core/_header.scss

@@ -28,35 +28,18 @@
   padding: 16px 16px 0 16px;
   will-change: transform;
 
-  display: -webkit-flex;
-  display: -ms-flexbox;
   display: flex;
-
-  -webkit-flex-direction: row;
-      -ms-flex-direction: row;
-          flex-direction: row;
-  -webkit-flex-wrap: nowrap;
-      -ms-flex-wrap: nowrap;
-          flex-wrap: nowrap;
-  -webkit-justify-content: flex-start;
-      -ms-flex-pack: start;
-          justify-content: flex-start;
-  -webkit-align-items: stretch;
-      -ms-flex-align: stretch;
-          align-items: stretch;
-  -ms-flex-line-pack: center;
-      -webkit-align-content: center;
-          align-content: center;
-
-  transition: -webkit-transform 0.233s cubic-bezier(0,0,0.21,1) 0.1s;
+  flex-direction: row;
+  flex-wrap: nowrap;
+  justify-content: flex-start;
+  align-items: stretch;
+  align-content: center;
   transition: transform 0.233s cubic-bezier(0,0,0.21,1) 0.1s;
 }
 
 .header--collapsed {
-  transition: -webkit-transform 0.233s cubic-bezier(0,0,0.21,1) 0.13s;
   transition: transform 0.233s cubic-bezier(0,0,0.21,1) 0.13s;
-  -webkit-transform: translateY(-56px);
-          transform: translateY(-56px);
+  transform: translateY(-56px);
 }
 
 .header__menu {
@@ -82,21 +65,16 @@
   font-weight: 400;
   font-size: 20px;
   margin: 0;
-  -webkit-flex: 1;
-      -ms-flex: 1;
-          flex: 1;
+  flex: 1;
 }
 
 @media(min-width: 600px) {
   .header {
     padding: 16px 32px 0 24px;
     height: 144px;
-    -webkit-flex-direction: column;
-      -ms-flex-direction: column;
-          flex-direction: column;
-
-          align-content: space-between;
-          align-items: flex-start;
+    flex-direction: column;
+    align-content: space-between;
+    align-items: flex-start;
   }
 
   .header__menu {
@@ -111,7 +89,6 @@
 
   .header--collapsed {
     transition: none;
-    -webkit-transform: none;
     transform: none;
   }
 }

src/styles/core/_side-nav.scss

@@ -55,13 +55,11 @@
       0 4px 8px rgba(0, 0, 0, .28);
 
   will-change: transform;
-  -webkit-transform: translateX(-102%);
-          transform: translateX(-102%);
+  transform: translateX(-102%);
 }
 
 
 .side-nav__content--animatable {
-  transition: -webkit-transform 0.233s cubic-bezier(0,0,0.21,1);
   transition: transform 0.233s cubic-bezier(0,0,0.21,1);
 }