Update bug report template

• Remove the "SPL Version" line, the repositories have been merged since the 0.8 release and we no longer need to ask about this.

• Simply ask for the kernel version / patch level and add a hint about how to get this information on Linux and FreeBSD.

• Remove "Status: Triage Needed" from the template, in practice we really haven't been using this label so let's step setting it.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: John Kennedy <john.kennedy@delphix.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes: #12340