kern: Don't need bsd.own.mk

Instead, replace it with bsd.init.mk and remove old comments about
FreeBSD 10.x compat. We used to need bsd.own.mk, but now can suffice
with bsd.init.mk since kern.opts.mk doesn't included that in too many
places.

Sponsored by:		Netflix

Author: bsdimp

sys/conf/dtb.build.mk

@@ -1,7 +1,3 @@
-
-.include <bsd.init.mk>
-# Grab all the options for a kernel build. For backwards compat, we need to
-# do this after bsd.own.mk.
 .include "kern.opts.mk"
 
 DTC?=		dtc

sys/conf/kern.opts.mk

@@ -4,6 +4,7 @@
 # parts to omit (eg CDDL or SOURCELESS_HOST). Some of these will cause
 # config.mk to define symbols in various opt_*.h files.
 
+
 #
 # Define MK_* variables (which are either "yes" or "no") for users
 # to set via WITH_*/WITHOUT_* in /etc/src.conf and override in the
@@ -13,17 +14,12 @@
 # that haven't been converted over.
 #
 
-# Note: bsd.own.mk must be included before the rest of kern.opts.mk to make
-# building on 10.x and earlier work. This should be removed when that's no
-# longer supported since it confounds the defaults (since it uses the host's
-# notion of defaults rather than what's default in current when building
-# within sys/modules).
-.include <bsd.own.mk>
-
 # These options are used by the kernel build process (kern.mk and kmod.mk)
 # They have to be listed here so we can build modules outside of the
 # src tree.
 
+.include <bsd.init.mk>
+
 KLDXREF_CMD?=	kldxref
 
 __DEFAULT_YES_OPTIONS = \