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/UM3NetworkPrinting/resources/svg/icons/Buildplate.svg

@@ -1,7 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- Generator: Adobe Illustrator 25.2.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
-<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">
-<path style="fill:#000E1A;" d="M18,21H6c-1.7,0-3-1.3-3-3V6c0-1.7,1.3-3,3-3h12c1.7,0,3,1.3,3,3v12C21,19.7,19.7,21,18,21z M5,19h14
-	V5H5V19z M14.7,7.7l-1.4-1.4l-7,7l1.4,1.4L14.7,7.7z M9.7,7.7L8.3,6.3l-2,2l1.4,1.4L9.7,7.7z"/>
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+<path d="M18,21H6c-1.7,0-3-1.3-3-3V6c0-1.7,1.3-3,3-3h12c1.7,0,3,1.3,3,3v12C21,19.7,19.7,21,18,21z M5,19h14
+	V5H5V19z M14.7,7.7l-1.4-1.4l-7,7l1.4,1.4L14.7,7.7z M9.7,7.7L8.3,6.3l-2,2l1.4,1.4L9.7,7.7z" />
 </svg>

plugins/UM3NetworkPrinting/resources/svg/icons/CameraPhoto.svg

@@ -1,8 +1,6 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- Generator: Adobe Illustrator 25.2.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
-<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">
-<path style="fill:#000E1A;" d="M19,6h-1.6l-2-2H8.6l-2,2H5C3.3,6,2,7.3,2,9v8c0,1.7,1.3,3,3,3h14c1.7,0,3-1.3,3-3V9
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 24 24">
+<path d="M19,6h-1.6l-2-2H8.6l-2,2H5C3.3,6,2,7.3,2,9v8c0,1.7,1.3,3,3,3h14c1.7,0,3-1.3,3-3V9
 	C22,7.3,20.7,6,19,6z M20,18H4V8h3.4l2-2h5.2l2,2H20V18z M12,8c-2.2,0-4,1.8-4,4s1.8,4,4,4s4-1.8,4-4S14.2,8,12,8z M12,14
-	c-1.1,0-2-0.9-2-2s0.9-2,2-2s2,0.9,2,2S13.1,14,12,14z"/>
+	c-1.1,0-2-0.9-2-2s0.9-2,2-2s2,0.9,2,2S13.1,14,12,14z" />
 </svg>

plugins/UM3NetworkPrinting/resources/svg/icons/Extruder.svg

@@ -1,15 +1,5 @@
 <?xml version="1.0" encoding="iso-8859-1"?>
-<!-- Generator: Adobe Illustrator 24.3.0, SVG Export Plug-In . SVG Version: 6.00 Build 0)  -->
-<svg version="1.1" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink" x="0px" y="0px"
-	 viewBox="0 0 30 30" style="enable-background:new 0 0 30 30;" xml:space="preserve">
-<g id="Layer_1">
-	<g>
-		<g>
-			<path d="M15,3C8.37,3,3,8.37,3,15v11h2v-4.36C7.15,24.87,10.83,27,15,27c6.63,0,12-5.37,12-12S21.63,3,15,3z M15,25
-				C9.49,25,5,20.51,5,15S9.49,5,15,5s10,4.49,10,10S20.51,25,15,25z"/>
-		</g>
-	</g>
-</g>
-<g id="Comments">
-</g>
+<svg version="1.1" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 30 30">
+<path d="M15,3C8.37,3,3,8.37,3,15v11h2v-4.36C7.15,24.87,10.83,27,15,27c6.63,0,12-5.37,12-12S21.63,3,15,3z M15,25
+	C9.49,25,5,20.51,5,15S9.49,5,15,5s10,4.49,10,10S20.51,25,15,25z"/>
 </svg>