debugfs: remove extra debugfs_create_file_unsafe() declaration

debugfs_create_file_unsafe() is declared twice in exactly the same
manner each: once in fs/debugfs/internal.h and once in
include/linux/debugfs.h

All files that include the former also include the latter and thus,
the declaration in fs/debugfs/internal.h is superfluous.

Remove it.

Signed-off-by: Nicolai Stange <nicstange@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>