dt-bindings: input: touschcreen: Remove sun4i documentation

This patch removes the sun4i touchscreen controller binding
documentation since it has been merged with the sun4i GPADC binding
documentation.
Signed-off-by: Quentin Schulz <quentin.schulz@free-electrons.com>
Acked-by: Rob Herring <robh@kernel.org>
Acked-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

Documentation/devicetree/bindings/input/touchscreen/sun4i.txt

-sun4i resistive touchscreen controller
---------------------------------------
-
-Required properties:
- - compatible: "allwinner,sun4i-a10-ts", "allwinner,sun5i-a13-ts" or
-   "allwinner,sun6i-a31-ts"
- - reg: mmio address range of the chip
- - interrupts: interrupt to which the chip is connected
- - #thermal-sensor-cells: shall be 0
-
-Optional properties:
- - allwinner,ts-attached	 : boolean indicating that an actual touchscreen
-				   is attached to the controller
- - allwinner,tp-sensitive-adjust : integer (4 bits)
-				   adjust sensitivity of pen down detection
-				   between 0 (least sensitive) and 15
-				   (defaults to 15)
- - allwinner,filter-type	 : integer (2 bits)
-				   select median and averaging filter
-				   samples used for median / averaging filter
-				   0: 4/2
-				   1: 5/3
-				   2: 8/4
-				   3: 16/8
-				   (defaults to 1)
-
-Example:
-
-	rtp: rtp@01c25000 {
-		compatible = "allwinner,sun4i-a10-ts";
-		reg = <0x01c25000 0x100>;
-		interrupts = <29>;
-		allwinner,ts-attached;
-		#thermal-sensor-cells = <0>;
-		/* sensitive/noisy touch panel */
-		allwinner,tp-sensitive-adjust = <0>;
-		allwinner,filter-type = <3>;
-	};