Remove devicetree-usage wiki page source
Remove devicetree-usage wiki page source

The document is now hosted on elinux.org

http://elinux.org/Device_Tree_Usage

Signed-off-by: Grant Likely <9069e6f5a2b566e2674a0ba1e2bf39c12c195fad@linaro.org>

kvekaria/devicetree-specification,devicetree-org/devicetree-specification