maint.mk: remove more coreutils-specific targets; XZ_OPT=-9ev

maint.mk: remove more coreutils-specific targets; XZ_OPT=-9ev

* top/maint.mk (cvs-check): Remove target; it was just an alias
to the better-named vc-diff-check.
(maintainer-distcheck): Remove rule.  It was used only from
the (alpha/beta/major) target, and all of its commands but one
were coreutils-specific.
(vc-dist): Remove rule.
(alpha beta major): Run "$(MAKE) distcheck" explicitly.
Run vc-diff-check, not vc-dist.
Run $(MAKE) dist with XZ_OPT=-9ev.  Note spelling, with "-".