Remove useless and unused SVG elements

- Remove unused imports of xlink.
- Remove comments about which application originally wrote the text file. It's untrue because PyCharm edited it, etc.
- Remove unused IDs.
- Remove unused colours for icons rendered with RecolorImage.
- Remove useless x and y positions on 0, which is the default.
- Remove useless style setting the background to transparent.
- Remove useless whitespace in the path d attribute, and remove the then-useless XML space preserving attribute.
- Remove unused groups.
- Remove unused CSS classes.

Contributes to issue CURA-8342.

plugins/PostProcessingPlugin/Script.svg

@@ -1,10 +1,6 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<svg version="1.1" id="Artwork" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
-	 viewBox="0 0 24 24" style="enable-background:new 0 0 24 24;" xml:space="preserve">
-<g>
-	<polygon style="fill:#1D1C1A;" points="4.4,12 8.2,15.8 6.8,17.2 1.6,12 6.8,6.8 8.2,8.2 	"/>
-	<polygon style="fill:#1D1C1A;" points="22.4,12 17.2,17.2 15.8,15.8 19.6,12 15.8,8.2 17.2,6.8 	"/>
-	
-		<rect x="3.9" y="11" transform="matrix(0.1236 -0.9923 0.9923 0.1236 -1.429 22.4317)" style="fill:#1D1C1A;" width="16.1" height="2"/>
-</g>
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+	<polygon points="4.4,12 8.2,15.8 6.8,17.2 1.6,12 6.8,6.8 8.2,8.2" />
+	<polygon points="22.4,12 17.2,17.2 15.8,15.8 19.6,12 15.8,8.2 17.2,6.8" />
+	<rect x="3.9" y="11" transform="matrix(0.1236 -0.9923 0.9923 0.1236 -1.429 22.4317)" width="16.1" height="2" />
 </svg>