staging: mt7621-dts: remove obsolete switch node

This was for OpenWrt's swconfig driver, which never made it upstream,
and was also superseded by MT7530 DSA driver.

Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: DENG Qingfang <dqfext@gmail.com>
Link: https://lore.kernel.org/r/20210108025155.31556-1-dqfext@gmail.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>