firmware: Drop FIRMWARE_IN_KERNEL Kconfig option

It doesn't actually do anything.  Merge its help text into
EXTRA_FIRMWARE.

Fixes: 5620a0d1aa ("firmware: delete in-kernel firmware")
Fixes: 0946b2fb38 ("firmware: cleanup FIRMWARE_IN_KERNEL message")
Signed-off-by: Benjamin Gilbert <benjamin.gilbert@coreos.com>
Signed-off-by: Robin H. Johnson <robbat2@gentoo.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/sh/configs/polaris_defconfig

@@ -38,7 +38,6 @@ CONFIG_IP_MULTICAST=y
 # CONFIG_INET_XFRM_MODE_BEET is not set
 # CONFIG_IPV6 is not set
 CONFIG_UEVENT_HELPER_PATH="/sbin/hotplug"
-# CONFIG_FIRMWARE_IN_KERNEL is not set
 CONFIG_MTD=y
 CONFIG_MTD_CMDLINE_PARTS=y
 CONFIG_MTD_BLOCK=y