lispy.el: use `preserve-names' for `help-function-arglist'

* lispy.el (lispy-debug-step-in): Update.

* lispy-inline.el (lispy--arglist): Update.
lispy.el (lispy-mark-list): take prefix arg
lispy.el (lispy-kill): fix

* lispy.el (lispy-kill): Remove deletion from one of the branches, kill
  instead.

* lispy-test.el (lispy-kill): Update test.