[no sq] Move shaders & remove dead Irrlicht tests (#15006)

* Move irrlicht shaders to correct place

* Remove unused Irrlicht tests

client/shaders/Irrlicht/Renderer2D.vsh

@@ -0,0 +1,24 @@
+#version 100
+
+/* Attributes */
+
+attribute vec4 inVertexPosition;
+attribute vec4 inVertexColor;
+attribute vec2 inTexCoord0;
+
+/* Uniforms */
+
+uniform float uThickness;
+
+/* Varyings */
+
+varying vec2 vTextureCoord;
+varying vec4 vVertexColor;
+
+void main()
+{
+	gl_Position = inVertexPosition;
+	gl_PointSize = uThickness;
+	vTextureCoord = inTexCoord0;
+	vVertexColor = inVertexColor.bgra;
+}