libxl: Remove libxl_tmem_destroy and associated xl command

libxl: Remove libxl_tmem_destroy and associated xl command

Dan Magenheimer explains in <4c2f7fca-dda2-4598-aaab-3a6a3fe532cd@default>:

	I think the tmem_destroy functionality pre-dates the
	existence of tmem "freeable" memory* and was a way for
	a toolset to force the hypervisor to free up the hypervisor
	memory used by some or all ephemeral tmem pools.  Once the
	tmem allocation/free process was directly linked into
	alloc_heap_pages() in the hypervisor (see call to
	tmem_relinquish_pages()), this forcing function was
	no longer needed.

	So, bottom line, I *think* it can be ripped out, or at least
	for now removed from the definition of the stable xl API/UI.
	The libxl.c routine libxl_tmem_destroy() could also be
	removed if you like, but I guess I'd prefer to leave the
	lower level droppings in xc.c and in the hypervisor in case
	I am misremembering.

Accordingly remove this interface from libxl and xl but don't touch libxc or
the hypervisor.

This is the only libxl_tmem_* function which might potentially have required
conversion to be asynchronous and which therefore might have been a potential
API stability concern.

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
Committed-by: Ian Jackson <ian.jackson.citrix.com>
Acked-by: Dan Magenheimer <dan.magenheimer@oracle.com>