remove rayon feature from i_overlay

[michaelkirk]

• [x] I agree to follow the project's code of conduct.

• [x] I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

Change in benchmarks were a mix of small wins and small losses (0-3%), with no discernible pattern.

[frewsxcv]

Oops I also just opened a PR https://github.com/georust/geo/pull/1250

[michaelkirk]

lets merge #1250 instead