include: env: ti_common: Remove findfdt from bootcmd_ti_mmc

include: env: ti_common: Remove findfdt from bootcmd_ti_mmc

findfdt is used by bootcmd_ti_mmc by default which used to help populate
the fdtfile. The users of findfdt from bootcmd_ti_mmc have migrated to
ti_set_fdt_env for populating fdtfile; Hence, findfdt can be removed from
bootcmd_ti_mmc having no-impact for any platform.

Remove findfdt to not print out the warning that gets set after calling
ti_set_fdt_env. viz.
"echo WARN: fdtfile already set. Stop using findfdt in script"

Signed-off-by: Dhruva Gole <d-gole@ti.com>
Signed-off-by: Manorit Chawdhry <m-chawdhry@ti.com>