tests/indent: change directive from '#' to '//'

Using a '//' instead of '#' turns the directives into well-formed C
code, resulting in fewer error markers in the editor.

indent: remove FreeBSD IDs

Most of the IDs were empty anyway.

indent: change product name, update version number

NetBSD's indent has deviated enough from FreeBSD's indent to warrant a
different product name. When indent was copied from FreeBSD in 2019,
that update introduced several new bugs, some of which have been fixed
in the NetBSD version.

NetBSD indent, unlike FreeBSD indent, supports C99 comments and C99
initializer designators.

tests/indent: migrate test for '--version' to t_options