dt-bindings: input: remove fsl-mma8450 which is handled by trivial-devices

trivial-devices.yaml already provide bindings for fsl-mma8450.
Since input/fsl-mma8450.txt provides no extra value, lets remove it.
Signed-off-by: Corentin Labbe <clabbe@baylibre.com>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
Link: https://lore.kernel.org/r/20210521192210.12839-1-clabbe@baylibre.comSigned-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>

Documentation/devicetree/bindings/input/fsl-mma8450.txt

-* Freescale MMA8450 3-Axis Accelerometer
-
-Required properties:
-- compatible : "fsl,mma8450".
-- reg: the I2C address of MMA8450
-
-Example:
-
-accelerometer: mma8450@1c {
-	compatible = "fsl,mma8450";
-	reg = <0x1c>;
-};