Remove onboarding from scope summary

[mmccool]

• This removes mention of "onboarding" from the charter scope summary
• This is to address some concerns raised (see issue What does "onboarding" involve? #67) about whether onboarding is something we should do in WoT or should be done in another group, whether we need some exploratory work first, etc.
• The exact wording of the text in the scope section after this PR means we still could do it, this PR just means we would not be committing to do it in the charter itself.
• I would still like to merge PR Expand description of Onboarding in Details #77 (and refine it) so we have a clear definition of what problem needs to be solved and a potential solution to that problem, even if we later spin off that work into the IG or another group. I have my doubts that some other group will solve this problem for us if we do nothing.
• While I was at it I got rid of a comma after "reusable" that was unnecessary and potentially confusing.

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