not-es6 rule for String#normalize triggers on Node#normalize

[edg2s]

Node#normalize is valid ES5, so shouldn't warn.

[MatmaRex]

For other similar conflicts, instead of "no-restricted-properties" we have rules using "no-restricted-syntax" which try to avoid the false positives, but I don't see a way to distinguish these two methods when just looking at the syntax. It might be okay to just document this limitation, and for users to selectively disable the check for each use of Node#normalize? If it's not okay, then I guess we'll have to remove this check.

[jdforrester]

Given that Node#normalize is so rare I think it's probably fine just to document it.

[jdforrester]

Ping. Do we want to just document it and leave it at that?

[Krinkle]

Sounds good to me. If it was a common method, perhaps the false negatives would outweigh the benefit of the true positives. But given it's rare, having to disable it in a few places and/or to opt-out the rule in a whole repo, seems worth it for everything else.