output/roar: remove

Bugs in libroar which broke the MPD build have been annoying me for
quite some time, and the newest bug has now hit my main build machine:

 https://github.com/MusicPlayerDaemon/MPD/issues/377

Problem is the usage of the typedef `_IO_off64_t` in libroar's
`vio_stdio.h`:

 int roar_vio_to_stdio_lseek (void *__cookie, _IO_off64_t *__pos, int __w);

This `_IO_off64_t` is an internal implementation detail of glibc and
was removed in version 2.28.  Nobody must ever use it.  Why the ****
did the RoarAudio developers use it?  Not using internal typedefs
isn't exactly rocket science.

This annoys me enough to finally remove the plugin.  Anyway, I've
never heard of anybody using RoarAudio, so my best guess is that
nobody will notice.

doc/plugins.rst

@@ -936,21 +936,6 @@ The pulse plugin connects to a `PulseAudio <http://www.freedesktop.org/wiki/Soft
    * - **sink NAME**
      - Specifies the name of the PulseAudio sink :program:`MPD` should play on.
 
-roar
-~~~~
-The roar plugin connects to a `RoarAudio <http://roaraudio.keep-cool.org/>`_ server.
-
-.. list-table::
-   :widths: 20 80
-   :header-rows: 1
-
-   * - Setting
-     - Description
-   * - **server HOSTNAME**
-     - The host name of the RoarAudio server. If not specified, then :program:`MPD` will connect to the default locations.
-   * - **role ROLE**
-     - The "role" that :program:`MPD` registers itself as in the RoarAudio server. The default is "music".
-
 recorder
 ~~~~~~~~
 The recorder plugin writes the audio played by :program:`MPD` to a file. This may be useful for recording radio streams.

doc/user.rst

@@ -72,7 +72,7 @@ For example, the following installs a fairly complete list of build dependencies
       libzzip-dev \
       libcurl4-gnutls-dev libyajl-dev libexpat-dev \
       libasound2-dev libao-dev libjack-jackd2-dev libopenal-dev \
-      libpulse-dev libroar-dev libshout3-dev \
+      libpulse-dev libshout3-dev \
       libsndio-dev \
       libmpdclient-dev \
       libnfs-dev libsmbclient-dev \