[ci skip] Remove obsolete note re: pre-upgrade attribute vs. property…

… priority

README.md

@@ -500,7 +500,6 @@ id is to use `id`.
 * <a name="breaking-created-timing"></a>The legacy `created` callback is no longer called before default values in `properties` have been set.  As such, you should not rely on properties set in `created` from within `value` functions that define property defaults.  However, you can now set _any_ property defaults within the `created` callback (in 1.0 this was forbidden for observed properties) in lieu of using the `value` function in `properties`.
 * <a name="breaking-boolean-attribute-binidng"></a>Binding a default value of `false` via an _attribute binding_ to a boolean property will not override a default `true` property of the target, due to the semantics of boolean attributes.  In general, property binding should always be used when possible, and will avoid such situations.
 * <a name="breaking-lazyRegister"></a>`lazyRegister` option removed and all meta-programming (parsing template, creating accessors on prototype, etc.) is deferred until the first instance of the element is created
-* <a name="breaking-attribute-property-timing"></a>Any attribute values will take priority over property values set prior to upgrade due to V1 `attributeChangedCallback` timing semantics.  In 1.x properties set prior to upgrade overrode attributes.
 * <a name="breaking-transpiling"></a>Polymer 2.0 uses ES2015 syntax, and can be run without transpilation in current Chrome, Safari 10, Safari Technology Preview, Firefox, and Edge.  Transpilation is required to run in IE11 and Safari 9.  We will be releasing tooling for development and production time to support this need in the future.
 * <a name="breaking-hostAttributes-class"></a>In Polymer 1.x, the `class` attribute was explicitly blacklisted from `hostAttributes` and never serialized. This is no longer the case using the 2.0 legacy API.
 * <a name="breaking-url-changes"></a>In Polymer 1.x, URLs in attributes and styles inside element templates were re-written to be relative to the element HTMLImport. Based on user feedback, we are changing this behavior.