board: mediatek: mt7622: remove board_late_init

The function board_late_init defined for mt7622 is useless now. Just
remove it.

diff --git a/board/mediatek/mt7622/mt7622_rfb.c b/board/mediatek/mt7622/mt7622_rfb.c
index e7f492a..9d24c8c 100644
--- a/board/mediatek/mt7622/mt7622_rfb.c
+++ b/board/mediatek/mt7622/mt7622_rfb.c
@@ -15,10 +15,3 @@
 {
 	return 0;
 }
-
-int board_late_init(void)
-{
-	gd->env_valid = 1; //to load environment variable from persistent store
-	env_relocate();
-	return 0;
-}