test defs: unindent without temporary file

test defs: unindent without temporary file

* tests/defs.in (commented_sed_unindent_prog): Commented Sed program
that strips the "proper" amount of leading whitespace.
(unindent): Lazily strip comments from the above program and use it
to unindent without using a temporary file.

Signed-off-by: Peter Rosin <peda@lysator.liu.se>