Remove m.prop + m.withAttr (#2317)

* Remove `m.prop` + `m.withAttr`

- For many uses, `m.withAttr` is *more* verbose than just directly using
  an event handler
- If you're using it with a bound callback, you're literally wasting a
  single character in the human readable version (and you're *saving*
  them in the minified output).
- It sometimes obscures your intent, if overused.
- Functions are easier to compress than `m.withAttr`, resulting in
  slightly smaller bundles.
- `m.withAttr` is overused anyways.
- `m.prop` is basically useless without `m.withAttr`, and the API
  doesn't have the same benefits it had with 0.2.x.

* Update changelog

docs/nav-methods.md

@@ -7,8 +7,6 @@
 	- [m.jsonp](jsonp.md)
 	- [m.parseQueryString](parseQueryString.md)
 	- [m.buildQueryString](buildQueryString.md)
-	- [m.withAttr](withAttr.md)
-	- [m.prop](prop.md)
 	- [m.trust](trust.md)
 	- [m.fragment](fragment.md)
 	- [m.redraw](redraw.md)