MFC r268945:

MFC	r268945:
Fix hdestroy() compliance issue.

The hcreate(3) implementation and related functions we inherited
from NetBSD used to free() the key value, something that is not
supported by the standard implementation.

This would cause a segmentation fault when attempting to run
the examples from the opengroup and linux manpages.

There is no need to bump the __FreeBSD_version as we have
always claimed XPG4.2 compliance but if some reference is
required, the bump for r269484 can be used.

Reference:
http://bugs.dragonflybsd.org/issues/1398

git-svn-id: svn://svn.freebsd.org/base/stable/10@269491 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f