configs/*: drop explicit BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_DEVTMPFS=y
Commit 7f1f9185e (system: default to devtmpfs for /dev) changed our default
for /dev handling, but didn't remove the explicit selection of devtmpfs from
a number of defconfigs.
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>