security: fs: make inode explicitly non-modular

The Makefile/Kconfig entry controlling compilation of this code is:

security/Makefile:obj-$(CONFIG_SECURITYFS)                += inode.o

security/Kconfig:config SECURITYFS
security/Kconfig:       bool "Enable the securityfs filesystem"

...meaning that it currently is not being built as a module by anyone.

Lets remove the couple traces of modular infrastructure use, so that
when reading the driver there is no doubt it is builtin-only.

We also delete the MODULE_LICENSE tag etc. since all that information
is already contained at the top of the file in the comments.

The removal of module.h uncovered a couple previously hidden implicit
header requirements which are now included explicitly.

Cc: James Morris <jmorris@namei.org>
Cc: "Serge E. Hallyn" <serge@hallyn.com>
Cc: linux-security-module@vger.kernel.org
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: James Morris <james.morris@microsoft.com>