Remove legacy PDF JSON interface.

chrome/browser/resources/chromeos/chromevox/manifest.json.jinja2

 {
 {%if key is defined %}
   "key": "{{key}}",
 {% endif %}
   "manifest_version": 2,
   "name": "__MSG_CHROMEVOX_NAME__",
   "version": "{{set_version}}",
   "description": "__MSG_CHROMEVOX_DESCRIPTION__",
 {% if is_guest_manifest == '1' %}
   "incognito": "split",
@@ skipping 17 matching lines @@
     "<all_urls>"
   ],
   "content_scripts": [
     {
       "matches": [ "<all_urls>" ],
       "exclude_globs": [
 {% if is_webstore is not defined %}
           "chrome-extension://*",
           "chrome://*",
           "https://accounts.google.com/embedded/setup/chromeos*",
-          "https://talkgadget.google.com/hangouts*"
+          "https://talkgadget.google.com/hangouts*",
+          "*.pdf"
 {% endif %}
       ],
       "all_frames": true,
       "js": [
 {% if is_js_compressed == '1' %}
         "chromeVoxChromePageScript.js",
         "chromeVox2ChromePageScript.js"
 {% else %}
         "closure/closure_preinit.js",
         "closure/base.js",
@@ skipping 46 matching lines @@
     }
   },
   "options_page": "chromevox/background/options.html",
   "default_locale": "en",
   "icons": {
     "16": "images/chromevox-16.png",
     "48": "images/chromevox-48.png",
     "128": "images/chromevox-128.png"
   }
 }