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

tests/test-api.js

@@ -45,16 +45,6 @@ o.spec("api", function() {
 			o(vnode.children[0].tag).equals("div")
 		})
 	})
-	o.spec("m.withAttr", function() {
-		o("works", function() {
-			var spy = o.spy()
-			var handler = m.withAttr("value", spy)
-
-			handler({currentTarget: {value: 10}})
-
-			o(spy.args[0]).equals(10)
-		})
-	})
 	o.spec("m.parseQueryString", function() {
 		o("works", function() {
 			var query = m.parseQueryString("?a=1&b=2")