Removed backend.sensor.ir.zeroborg.

That code is very old and broken, and it covers a very marginal feature
(events from the IR sensor of a Zeroborg board) that can be easily
covered by any general-purpose IR sensors.

docs/source/backends.rst

@@ -15,7 +15,6 @@ Backends
     platypush/backend/music.spotify.rst
     platypush/backend/nodered.rst
     platypush/backend/redis.rst
-    platypush/backend/sensor.ir.zeroborg.rst
     platypush/backend/stt.deepspeech.rst
     platypush/backend/stt.picovoice.hotword.rst
     platypush/backend/stt.picovoice.speech.rst

docs/source/platypush/backend/sensor.ir.zeroborg.rst

@@ -1,6 +0,0 @@
-``sensor.ir.zeroborg``
-========================================
-
-.. automodule:: platypush.backend.sensor.ir.zeroborg
-    :members:
-