feat: allow specifying a hook with removeHook()

[davecardwell]

Summary

This pull request implements an optional second argument to removeHook() to allow specifying the hook function to remove.

Background & Context

Currently you can only pop hooks off the stack.

It’s a pretty straight-forward implementation and non-breaking change to allow for specifying the hook to remove.

Because DOMPurify’s hooks are global it is otherwise difficult to write code with multiple paths that may be adding hooks and tidying up after themselves. Now it can be trivially written like:

try {
  DOMPurify.addHook('afterSanitizeElements', myHook);

  // …
} finally {
  DOMPurify.removeHook('afterSanitizeElements', myHook);
}

Tasks

• Review implementation changes
• Confirm new test is sufficient

[cure53]

This looks great, thank you very much :)