of/fdt: remove unused of_scan_flat_dt_by_path

of_scan_flat_dt_by_path is unused anywhere in the kernel, so remove it.

Signed-off-by: Rob Herring <robh@kernel.org>
Tested-by: Michal Simek <michal.simek@xilinx.com>
Tested-by: Grant Likely <grant.likely@linaro.org>
Tested-by: Stephen Chivers <schivers@csc.com>