Prefer seq-random-elt to nth+random

Prefer seq-random-elt to nth+random

* lisp/emacs-lisp/seq.el (seq-random-elt): Autoload.
* lisp/avoid.el (mouse-avoidance-random-shape):
* lisp/epa-ks.el (epa-ks--query-url):
* lisp/erc/erc-networks.el (erc-server-select):
* lisp/gnus/gnus-fun.el (gnus--random-face-with-type)
(gnus-fun-ppm-change-string):
* lisp/net/soap-inspect.el (soap-sample-value-for-xs-simple-type):
* lisp/obsolete/landmark.el (landmark-random-move):
* lisp/play/mpuz.el (mpuz-build-random-perm):
* lisp/play/zone.el (zone-pgm-stress):
* lisp/vc/add-log.el (add-change-log-entry):
* test/lisp/net/tramp-tests.el
(tramp-test44-asynchronous-requests): Prefer seq-random-elt to
nth+random.