Editorial: Remove important terms from CORE-AAM

[spectranaut]

There were only two important terms listed in CORE-AAM, and one of them had no references. The other was only used in one table, so I moved the definition to above the table.

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[spectranaut]

Thanks Rahim, for the thoughts/thoroughness! But there is no reference to anything like activation behavior in the events section, so from my perspective, there is no reason to include it. You got me curious about what that term was originally used for -- so I looked up the commit that added it: https://github.com/w3c/core-aam/pull/92/files

@jnurthen -- you added the term activation behavior.. but even when you added it, there was no reference to it in the spec. Do you know why? Is it ok to remove?

[spectranaut]

@rahimabdi can you see my comment and re-review this PR?