specs: don't automatically add final newline to tmp files.

While some UNIX utilities require source files to end every line
with a '\n', Emacs and Zemacs do not.  And we might like to have
examples that specify behaviour with non-'\n' ending files.
* lib/zemacs/specs/spec_helper.lua (mktmpfile): Don't append
a newline to temporary file contents.
* lib/zemacs/specs/zlisp_buffer_spec.yaml,
lib/zemacs/specs/zlisp_move_spec.yaml: Adjust accordingly.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>