Align SVGs to WikimediaUI color palette and optimize

Aligning SVGs to WikimediaUI color palette, optimizing
by help of SVGO and align markup to each other, among changes:
- unifying XML declaration
- removing `standalone=no` as it's default
- adding `viewBox` attribute for cross-browser compatibility
- removing unnecessary groups and ids where applicable
- unifying identation
- bringing attributes in order

Bug: T178867
Change-Id: Ie7803dd904cee14fa401331e082982794dc0a225

resources/images/back-grey-rtl.svg

@@ -1,4 +1,4 @@
-<?xml version="1.0" encoding="UTF-8" standalone="no"?>
-<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24" id="Layer_1">
-    <path d="M7 4c-.8.8-.8 2.2 0 3l6 6-6 6c-.8.8-.8 2.2 0 3l9-9-9-9z" id="path3" fill="#555"/>
+<?xml version="1.0" encoding="UTF-8"?>
+<svg xmlns="http://www.w3.org/2000/svg" width="24" height="24" viewBox="0 0 24 24">
+	<path fill="#54595d" d="M7 4c-.8.8-.8 2.2 0 3l6 6-6 6c-.8.8-.8 2.2 0 3l9-9-9-9z"/>
 </svg>