dt-bindings: arm: imx: scu: drop deprecated legacy clock binding

The legacy clock binding are not maintained anymore. It has only
a very preliminary supported clocks during initial upstream and
meaningless for users. So drop it from binding doc now.

Cc: devicetree@vger.kernel.org
Signed-off-by: Dong Aisheng <aisheng.dong@nxp.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@nxp.com>

Documentation/devicetree/bindings/arm/freescale/fsl,scu.txt

@@ -89,10 +89,8 @@ Required properties:
 			  "fsl,imx8qm-clk"
 			  "fsl,imx8qxp-clk"
 			followed by "fsl,scu-clk"
-- #clock-cells:		Should be either
-			2: Contains the Resource and Clock ID value.
-			or
-			1: Contains the Clock ID value. (DEPRECATED)
+- #clock-cells:		Should be 2.
+			Contains the Resource and Clock ID value.
 - clocks:		List of clock specifiers, must contain an entry for
 			each required entry in clock-names
 - clock-names:		Should include entries "xtal_32KHz", "xtal_24MHz"