text/template: revert CL 66410 "add break, continue actions in ranges"

The new break and continue actions do not work in html/template, and
fixing them requires thinking about security issues that seem too
tricky at this stage of the release. We will try again for 1.11.

Original CL description:

    text/template: add break, continue actions in ranges

    Adds the two range control actions "break" and "continue". They act the
    same as the Go keywords break and continue, but are simplified in that
    only the innermost range statement can be broken out of or continued.

    Fixes #20531

Updates #20531
Updates #23683

Change-Id: Ia7fd3c409163e3bcb5dc42947ae90b15bdf89853
Reviewed-on: https://go-review.googlesource.com/92155


Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Russ Cox <rsc@golang.org>