[][Remove mt7981 u3 support in sgmii2 2.5g wan dts]

[Description]
Remove mt7981 u3 support in sgmii2 2.5g wan dts

[Release-log]
N/A

Change-Id: Ie0f2f845551d52ebc920cb228ccd05d29102b82c
Reviewed-on: https://gerrit.mediatek.inc/c/openwrt/feeds/mtk_openwrt_feeds/+/5331161
1 file changed