Bug 1585907 part 1: Remove exposure of the "reader" accessibility object attribute. r=Gijs

This reverts bug 1425541.
This was intended to make it easy for accessibility clients to retrieve the Reader View state programmatically.
However, it was never actually used by any clients.

Differential Revision: https://phabricator.services.mozilla.com/D48035

--HG--
extra : moz-landing-system : lando

browser/modules/ReaderParent.jsm

@@ -78,10 +78,6 @@ var ReaderParent = {
     let button = win.document.getElementById("reader-mode-button");
     let menuitem = win.document.getElementById("menu_readerModeItem");
     let key = win.document.getElementById("key_toggleReaderMode");
-    // aria-reader is not a real ARIA attribute. However, this will cause
-    // Gecko accessibility to expose the "reader" object attribute. We do this
-    // so that the reader state is easy for accessibility clients to access
-    // programmatically.
     if (browser.currentURI.spec.startsWith("about:reader")) {
       let closeText = gStringBundle.GetStringFromName("readerView.close");
 
@@ -98,7 +94,6 @@ var ReaderParent = {
 
       key.setAttribute("disabled", false);
 
-      browser.setAttribute("aria-reader", "active");
       Services.obs.notifyObservers(null, "reader-mode-available");
     } else {
       let enterText = gStringBundle.GetStringFromName("readerView.enter");
@@ -117,10 +112,7 @@ var ReaderParent = {
       key.setAttribute("disabled", !browser.isArticle);
 
       if (browser.isArticle) {
-        browser.setAttribute("aria-reader", "available");
         Services.obs.notifyObservers(null, "reader-mode-available");
-      } else {
-        browser.removeAttribute("aria-reader");
       }
     }
   },