ath79: remove AT803X config symbol from subtargets

The AT803X_PHY kernel config symbol is already enabled target-wide. SO
it does not have to be enabled for individual subtargets.

Signed-off-by: David Bauer <[email protected]>

target/linux/ath79/generic/config-default

@@ -1,4 +1,3 @@
-CONFIG_AT803X_PHY=y
 CONFIG_BCM_NET_PHYLIB=y
 CONFIG_BROADCOM_PHY=y
 CONFIG_GPIO_PCA953X=y

target/linux/ath79/mikrotik/config-default

@@ -1,4 +1,3 @@
-CONFIG_AT803X_PHY=y
 CONFIG_CRC16=y
 CONFIG_CRYPTO_DEFLATE=y
 CONFIG_GPIO_LATCH=y