Always leave isTrusted as true when firing events

<form>.reset() always sets isTrusted in current implementations, so we
remove the spec language that sometimes set it to false.

One cannot trigger “send select update notifications” from script, so
the spec language that sometimes sets isTrusted to false for those
events can never be triggered, and is thus be removed.

Fixes whatwg#1912.

source

@@ -48687,20 +48687,13 @@ interface <dfn>HTMLSelectElement</dfn> : <span>HTMLElement</span> {
   a task</span>, using the <span>user interaction task source</span>, to run these steps:</p>
 
   <ol>
-   <li><p>Let <var>isTrusted</var> be false, if the <span>JavaScript execution context stack</span>
-   is not empty, and true otherwise.</p></li>
-
    <li><p><span data-x="concept-event-fire">Fire an event</span> named <code
    data-x="event-input">input</code> at the <code>select</code> element, with the <code
-   data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true and the <code
-   data-x="dom-Event-isTrusted">isTrusted</code> attribute initialized to
-   <var>isTrusted</var>.</p></li>
+   data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true.</p></li>
 
    <li><p><span data-x="concept-event-fire">Fire an event</span> named <code
    data-x="event-change">change</code> at the <code>select</code> element, with the <code
-   data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true and the <code
-   data-x="dom-Event-isTrusted">isTrusted</code> attribute initialized to
-   <var>isTrusted</var>.</p></li>
+   data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true.</p></li>
   </ol>
 
   <p>The <span data-x="concept-form-reset-control">reset algorithm</span> for <code>select</code>
@@ -55513,15 +55506,10 @@ fur
   data-x="concept-form-reset">reset</dfn>, run these steps:</p>
 
   <ol>
-   <li><p>Let <var>isTrusted</var> false, if this algorithm is invoked by the <code
-   data-x="dom-form-reset">reset()</code> method, and true otherwise.</p></li>
-
    <li><p>Let <var>reset</var> be the result of <span data-x="concept-event-fire">firing an
    event</span> named <code data-x="event-reset">reset</code> at <var>form</var>, with the <code
-   data-x="dom-Event-bubbles">bubbles</code> attribute initialized to true, <code
-   data-x="dom-Event-cancelable">cancelable</code> attribute initialized to true, and <code
-   data-x="dom-Event-isTrusted">isTrusted</code> attribute initialized to
-   <var>isTrusted</var>.</p></li>
+   data-x="dom-Event-bubbles">bubbles</code> and <code
+   data-x="dom-Event-cancelable">cancelable</code> attributes initialized to true.</p></li>
 
    <li><p>If <var>reset</var> is true, then invoke the <span
    data-x="concept-form-reset-control">reset algorithm</span> of each <span