Fix metal depth clear shader

Shaders/common/metal/clear_pass_depth.frag.glsl

@@ -1,7 +1,6 @@
 #version 330
 in vec2 texCoord;
 out vec4 fragColor;
-uniform vec4 clearColor;
 void main() {
-	fragColor = clearColor;
+	gl_FragDepth = 1.0;
 }