Finish excising electric indent from `open-line'

Finish excising electric indent from `open-line'

* lisp/simple.el (open-line): Remove INTERACTIVE argument.

* test/automated/simple-test.el (open-line-indent, open-line-hook):
  Adjust accordingly.

This change finishes what my commit of Thu Nov 19 17:32:37 2015 -0600
(git commit c59353896) started.  It turns out that having INTERACTIVE
cause `post-self-insert-hook' to run (via `newline') meant `open-line'
still had the electric indent behavior, as `post-self-insert-hook'
normally contains `electric-indent-post-self-insert-function' ever
since `electric-indent-mode' has been on by default.  Tracing the code
change in `open-line' is mildly twisty, because Artur Malabarba's
earliest two commits of 24 Oct 2015 first removed the `interactive'
form entirely (git commit 6939896e2) and then restored it with the new
extra "p" already added (git commit bd4f04f86), such that there is no
single-commit diff in which one sees the second "p" appear.  Thus this
change is effectively a reversion of parts of each of those commits.

This could close bug#21884, at least until further discussion.