Use current face foreground for SVG icons in customize

It turns out these few icons were missed when the color and size
information was removed from the SVG icons that replaced XPM icons for
Customize buffer.
* etc/images/down.svg:
* etc/images/left.svg:
* etc/images/right.svg:
* etc/images/up.svg: Don't define foreground; this means they will use
the foreground of the currently defined face instead.  (Bug#51556)

(cherry picked from commit 11702a6dd7)

etc/images/down.svg

@@ -25,7 +25,7 @@
   <title id='title8473'>Gnome Symbolic Icons</title>
   <defs id='defs7386'/>
   <g inkscape:groupmode='layer' id='layer10' inkscape:label='ui' transform='translate(-152.00586,-952)'>
-    <path inkscape:connector-curvature='0' d='m 166,957 -5.99414,5.99999 L 154,957 Z' id='path6424' sodipodi:nodetypes='cccc' style='fill:#2e3436;fill-opacity:1;stroke:none'/>
+    <path inkscape:connector-curvature='0' d='m 166,957 -5.99414,5.99999 L 154,957 Z' id='path6424' sodipodi:nodetypes='cccc' style='fill-opacity:1;stroke:none'/>
   </g>
   <g inkscape:groupmode='layer' id='layer1' inkscape:label='status' transform='translate(-152.00586,-888)'/>
   <g inkscape:groupmode='layer' id='layer11' inkscape:label='legacy' transform='translate(-152.00586,-952)'/>

etc/images/left.svg

@@ -25,7 +25,7 @@
   <title id='title8473'>Gnome Symbolic Icons</title>
   <defs id='defs7386'/>
   <g inkscape:groupmode='layer' id='layer10' inkscape:label='ui' transform='translate(-92.005848,-951.99999)'>
-    <path inkscape:connector-curvature='0' d='M 103,966 97.00585,959.99999 103,954 Z' id='path6400' sodipodi:nodetypes='cccc' style='fill:#2e3436;fill-opacity:1;stroke:none'/>
+    <path inkscape:connector-curvature='0' d='M 103,966 97.00585,959.99999 103,954 Z' id='path6400' sodipodi:nodetypes='cccc' style='fill-opacity:1;stroke:none'/>
   </g>
   <g inkscape:groupmode='layer' id='layer1' inkscape:label='status' transform='translate(-92.005848,-887.99999)'/>
   <g inkscape:groupmode='layer' id='layer11' inkscape:label='legacy' transform='translate(-92.005848,-951.99999)'/>

etc/images/right.svg

@@ -25,7 +25,7 @@
   <title id='title8473'>Gnome Symbolic Icons</title>
   <defs id='defs7386'/>
   <g inkscape:groupmode='layer' id='layer10' inkscape:label='ui' transform='translate(-112.00585,-951.99999)'>
-    <path inkscape:connector-curvature='0' d='m 117,966 6.00585,-6.00001 L 117,954 Z' id='path6412' sodipodi:nodetypes='cccc' style='fill:#2e3436;fill-opacity:1;stroke:none'/>
+    <path inkscape:connector-curvature='0' d='m 117,966 6.00585,-6.00001 L 117,954 Z' id='path6412' sodipodi:nodetypes='cccc' style='fill-opacity:1;stroke:none'/>
   </g>
   <g inkscape:groupmode='layer' id='layer1' inkscape:label='status' transform='translate(-112.00585,-887.99999)'/>
   <g inkscape:groupmode='layer' id='layer11' inkscape:label='legacy' transform='translate(-112.00585,-951.99999)'/>

etc/images/up.svg

@@ -25,7 +25,7 @@
   <title id='title8473'>Gnome Symbolic Icons</title>
   <defs id='defs7386'/>
   <g inkscape:groupmode='layer' id='layer10' inkscape:label='ui' transform='translate(-132.00585,-952)'>
-    <path inkscape:connector-curvature='0' d='M 146,963 140.00585,956.99999 134,963 Z' id='path6418' sodipodi:nodetypes='cccc' style='fill:#2e3436;fill-opacity:1;stroke:none'/>
+    <path inkscape:connector-curvature='0' d='M 146,963 140.00585,956.99999 134,963 Z' id='path6418' sodipodi:nodetypes='cccc' style='fill-opacity:1;stroke:none'/>
   </g>
   <g inkscape:groupmode='layer' id='layer1' inkscape:label='status' transform='translate(-132.00585,-888)'/>
   <g inkscape:groupmode='layer' id='layer11' inkscape:label='legacy' transform='translate(-132.00585,-952)'/>