drop "json-object" blocks: deprecated in Pygments 2.8

Given comments in pygments/pygments#1600, the
json-object lexer is geting deprecated with the upcoming Pygments 2.8,
and will fall back to "json".

At the same time, Pygments 2.8 comes with a new JSON parser that allows
for partial blocks missing surrounding curly braces, which is exactly
the use case we have in this documentation. Nice update!

source/features/security.rst

@@ -149,7 +149,7 @@ This is fine for initial stages of application development, but before deploying
 
 To enable Secure WebSocket, edit the main KMS configuration file (``/etc/kurento/kurento.conf.json``), and un-comment the following lines:
 
-.. code-block:: json-object
+.. code-block:: json
 
    "secure": {
      "port": 8433,

source/project/relnotes/v6_10_0.rst

@@ -142,7 +142,7 @@ New JSON settings parser
 
 Kurento uses the JSON parser that comes with the Boost C++ library; this parser accepted comments in JSON files, so we could comment out some lines when needed. The most common example of this was to force using only VP8 or H.264 video codecs in the Kurento settings file, ``/etc/kurento/modules/kurento/SdpEndpoint.conf.json``:
 
-.. code-block:: json-object
+.. code-block:: json
 
    "videoCodecs" : [
      {
@@ -155,7 +155,7 @@ Kurento uses the JSON parser that comes with the Boost C++ library; this parser
 
 This is the default form of the mentioned file, allowing Kurento to use either VP8 or H.264, as needed. To disable VP8, this would change as follows:
 
-.. code-block:: json-object
+.. code-block:: text
 
    "videoCodecs" : [
    //  {
@@ -172,7 +172,7 @@ However, starting from `Boost version 1.59.0 <https://www.boost.org/users/histor
 
 The devised workaround has been to allow inline comment characters inside the JSON attribute fields, so the former comment can now be done like this:
 
-.. code-block:: json-object
+.. code-block:: json
 
    "videoCodecs": [
        { "//name": "VP8/90000" },

source/user/writing_modules.rst

@@ -301,7 +301,7 @@ Run this from the root directory of your module:
 
 This generates a ``build/js/`` directory, containing all the client code. You can now manually copy this code to your application. Alternatively, you can use :term:`Bower` (for *Browser JavaScript*) or :term:`NPM` (for *Node.js*). To do that, you should add your JavaScript module as a dependency in your *bower.json* or *package.json* file, respectively:
 
-.. code-block:: json-object
+.. code-block:: json
 
    "dependencies": {
      "modulename": "0.0.1"