tomoyo: avoid unneeded creation of builtin-policy.h

When CONFIG_SECURITY_TOMOYO_INSECURE_BUILTIN_SETTING=y,
builtin-policy.h is unneeded.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>