Grow: fix check_reshape and open_code it.

Grow: fix check_reshape and open_code it.

check_reshape should not try to parse the subarray string - only
metadata handlers are allowed to do that.

The common code and only interpret a subarray string by passing it to
"container_content" which will then return only the member for that
subarray.

So remove check_reshape and place similar logic explicitly at the two
call-sites.  They are different enough that it is probably clearer to
have explicit code.

Signed-off-by: NeilBrown <neilb@suse.de>