doc: remove subsystem from pull request template
Remove request that user provide a list of subsystems in the pull request template.
- We already ask them to put the subsystems in the first line of the commit message.
- The subsystem is usually easy to determine.
- We have a bot that applies subsystem labels on new PRs and it seems to do a rather good job. Tools over rules. Let the bot do it.
- The fewer unnecessary things we ask for in the template, the lower the barrier to entry.
- Anecdotal, but I have never found it useful to have the person submitting the PR list out subsystems in the pull request post.
Checklist
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documentation is changed or added -
commit message follows commit guidelines
Affected core subsystem(s)
doc