net: dsa: mt7530: remove redundant MODULE_ALIAS entries

MODULE_ALIAS exports information to allow the module to be auto-loaded at
boot for the drivers registered using legacy platform registration.

However, currently the driver is always used by DT-only platform,
MODULE_ALIAS is redundant and should be removed properly.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>