mediatek: mt7623: drop RAMFS_COPY_BIN

fwtool is now always part of the sysupgrade stage2 ramdisk, so drop
the no longer needed RAMFS_COPY_BIN variable.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>

target/linux/mediatek/mt7623/base-files/lib/upgrade/platform.sh

-
 REQUIRE_IMAGE_METADATA=1
-RAMFS_COPY_BIN='fwtool'
 
 # Legacy full system upgrade including preloader for MediaTek SoCs on eMMC or SD
 legacy_mtk_mmc_full_upgrade() {