[Combobox] Remove escape-regexp dependency

[indiesquidge]

Summary

The escape-regexp package fails approval when trying to detect the license under which the project is distributed.

The package has not been touched in 7 years, and implements a single-line function that can be copied directly into source.

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• Other: removes unnecessary old dependency

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[indiesquidge]

@chancestrickland I don't mean to be a nuisance but I was wondering if Reach planned on doing a release soon. Unfortunately my company's use of Combobox is blocked in the CI build until this commit is out.

I'd be more than happy to help with testing releases and/or writing up release notes :)

[chaance]

@indiesquidge Planning on a weekend release with what's merged so far and (hopefully) a few more additions. I've got a handful of TODO comments sprinkled throughout, and more tests modeled after what I have set up currently are always greatly appreciated. I'm still not an expert when it comes to the quirks and nuances of Jest and JS DOM, so you may find some low-hanging fruit in the todos there.

I'm realizing that we could probably get more done with some help, but I need to actively provide guidelines and plans to make that happen!