ath79: drop unused mtd splitter

Neither the seama nor the wrgg splitter are used at the moment. Drop
them for now to not bloat the target from the beginning.

Signed-off-by: Mathias Kresin <[email protected]>

target/linux/ath79/config-4.14

@@ -168,10 +168,8 @@ CONFIG_MTD_PHYSMAP=y
 CONFIG_MTD_SPI_NOR=y
 CONFIG_MTD_SPLIT_FIRMWARE=y
 CONFIG_MTD_SPLIT_LZMA_FW=y
-CONFIG_MTD_SPLIT_SEAMA_FW=y
 CONFIG_MTD_SPLIT_TPLINK_FW=y
 CONFIG_MTD_SPLIT_UIMAGE_FW=y
-CONFIG_MTD_SPLIT_WRGG_FW=y
 CONFIG_MTD_TPLINK_PARTS=y
 CONFIG_MTD_VIRT_CONCAT=y
 CONFIG_NEED_DMA_MAP_STATE=y