btrfs: show compiled-in config features at module load time

We want to know if there are debugging features compiled in, this may
affect performance. The message is printed before the sanity checks.
Also kill version.h file that serves no purpose, we don't use any
version tag for kernel module.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>