Remove old icons

Signed-off-by: Šimon Brandner <simon.bra.ag@gmail.com>

res/img/feather-customised/maximize.svg

@@ -1,24 +0,0 @@
-<svg xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:cc="http://creativecommons.org/ns#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:svg="http://www.w3.org/2000/svg" xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd" xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape" width="18" height="18" viewBox="0 0 18 18" fill="none" stroke="currentColor" stroke-width="2">
-  <polyline
-     points="15 3 21 3 21 9"
-     id="polyline2"
-     transform="matrix(0.60029695,0,0,0.59437231,1.7964367,1.8097068)" />
-  <polyline
-     points="9 21 3 21 3 15"
-     id="polyline4"
-     transform="matrix(0.60029695,0,0,0.59437231,1.7964367,1.8097068)" />
-  <line
-     x1="14.402673"
-     y1="3.5928237"
-     x2="10.200594"
-     y2="7.7534299"
-     id="line6"
-     style="stroke-width:1.19465" />
-  <line
-     x1="3.5973275"
-     y1="14.291526"
-     x2="7.7994061"
-     y2="10.130919"
-     id="line8"
-     style="stroke-width:1.19465" />
-</svg>

res/img/feather-customised/minimize.svg

@@ -1,24 +0,0 @@
-<svg xmlns:dc="http://purl.org/dc/elements/1.1/" xmlns:cc="http://creativecommons.org/ns#" xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:svg="http://www.w3.org/2000/svg" xmlns="http://www.w3.org/2000/svg" xmlns:sodipodi="http://sodipodi.sourceforge.net/DTD/sodipodi-0.dtd" xmlns:inkscape="http://www.inkscape.org/namespaces/inkscape" width="18" height="18" viewBox="0 0 18 18" fill="none" stroke="currentColor" stroke-width="2">
-  <polyline
-     points="4 14 10 14 10 20"
-     id="polyline2"
-     transform="matrix(0.60000002,0,0,0.6,1.8000002,1.8000004)" />
-  <polyline
-     points="20 10 14 10 14 4"
-     id="polyline4"
-     transform="matrix(0.60000002,0,0,0.6,1.8000002,1.8000004)" />
-  <line
-     x1="10.200001"
-     y1="7.8000002"
-     x2="14.4"
-     y2="3.6000004"
-     id="line6"
-     style="stroke-width:1.2" />
-  <line
-     x1="3.6000001"
-     y1="14.4"
-     x2="7.8000007"
-     y2="10.2"
-     id="line8"
-     style="stroke-width:1.2" />
-</svg>