Issue #1751 - Remove Mac code behind MOZ_WIDGET_TOOLKIT == 'cocoa'

toolkit/themes/osx/global/tree/arrow-disclosure.svg

@@ -1,28 +0,0 @@
-<!-- This Source Code Form is subject to the terms of the Mozilla Public
-   - License, v. 2.0. If a copy of the MPL was not distributed with this
-   - file, You can obtain one at http://mozilla.org/MPL/2.0/. -->
-<svg width="16" height="16" viewBox="0 0 16 16" xmlns="http://www.w3.org/2000/svg">
-
-  <style>
-    .icon:not(:target) {
-      display: none;
-    }
-
-    .icon {
-      fill: #8c8c8c;
-    }
-
-    .icon.white {
-      fill: #fff;
-    }
-  </style>
-
-  <polygon id="arrow-disclosure-collapsed" class="icon" points="4,4  12,8.5  4,13" />
-  <polygon id="arrow-disclosure-collapsed-rtl" class="icon" points="4,8.5  12,4  12,13" />
-  <polygon id="arrow-disclosure-collapsed-inverted" class="icon white" points="4,4  12,8.5  4,13" />
-  <polygon id="arrow-disclosure-collapsed-inverted-rtl" class="icon white" points="4,8.5  12,4  12,13" />
-
-  <polygon id="arrow-disclosure-expanded" class="icon" points="3,5  12,5  7.5,13" />
-  <polygon id="arrow-disclosure-expanded-inverted" class="icon white" points="3,5  12,5  7.5,13" />
-
-</svg>