4.0.0

Change

• 9e86da1 Update @types/unist
  migrate: update too
• ec2db08 Change to require Node.js 16
  migrate: update too
• b2d67dd Change to use export map
  migrate: don’t use private APIs
• 32d3139 Change to return undefined, never test tree
  migrate: the tree is changed, so its nonsensical to also return it
  if you might want to remove tree itself, test that yourself with unist-util-is
• b63722b Change to remove RemoveOptions type
  migrate: RemoveOptions -> Options

Full Changelog: 3.1.1...4.0.0