maint/dev ~ remove 'fsevents' hack for npm clean-install (with notes)

- `npm clean-install` now requires at least NodeJS v10.23.1, npm v7.24.2 or yarn v1.22.19
- note: `npm install` continues to work for earlier versions of NodeJS/npm/yarn

## ref

- [npm ERR! fsevents not accessible from chokidar](bahmutov/npm-install#103)

package.json

@@ -237,9 +237,7 @@
 		"typescript": "~4.2.0",
 		"unified": "^9.2.0"
 	},
-	"optionalDependencies:#": "* 'fsevents' included to avoid `npm ci` errors with early npm versions; ref: <https://github.com/bahmutov/npm-install/issues/103>",
 	"optionalDependencies": {
-		"fsevents": "*"
 	},
 	"ava": {
 		"files": [