dt-bindings: arm,coresight-cti: Drop type for 'cpu' property

'cpu' has been added as a single phandle type to dtschema, so drop the
type here.
Reviewed-by: Mike Leach <mike.leach@linaro.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230925220511.2026514-1-robh@kernel.orgSigned-off-by: Rob Herring <robh@kernel.org>

Documentation/devicetree/bindings/arm/arm,coresight-cti.yaml

@@ -92,7 +92,6 @@ properties:
     maxItems: 1
 
   cpu:
-    $ref: /schemas/types.yaml#/definitions/phandle
     description:
       Handle to cpu this device is associated with. This must appear in the
       base cti node if compatible string arm,coresight-cti-v8-arch is used,