KeyboardEvent: Remove locale

In Firefox 58 and Chromium 64, a KeyboardEvent's `locale` property
returns `undefined`.

See also https://bugs.chromium.org/p/chromium/issues/detail?id=168971#c25

Author: tindzk

src/main/scala/org/scalajs/dom/raw/lib.scala

@@ -2665,17 +2665,6 @@ class KeyboardEvent(typeArg: String, keyboardEventInit: KeyboardEventInit)
    */
   def location: Int = js.native
 
-  /**
-   * A locale string indicating the locale the keyboard is configured for. This may
-   * be the empty string if the browser or device doesn't know the keyboard's locale.
-   *
-   * Note: This does not describe the locale of the data being entered. A user may
-   * be using one keyboard layout while typing text in a different language.
-   *
-   * MDN
-   */
-  def locale: String = js.native
-
   /**
    * The key value of the key represented by the event. If the value has a printed
    * representation, this attribute's value is the same as the char attribute.