dt-bindings: mtd: Drop object types when referencing other files

Setting an object type is redundant when a reference is made, so drop
these useless lines.
Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/linux-mtd/20221114090315.848208-17-miquel.raynal@bootlin.com

Documentation/devicetree/bindings/mtd/mtd.yaml

@@ -43,7 +43,6 @@ patternProperties:
     deprecated: true
 
   "^otp(-[0-9]+)?$":
-    type: object
     $ref: ../nvmem/nvmem.yaml#
 
     description: |