Remove CTC decoder prototype message (#2459)

Summary:
ctc decoder has been moved to beta, remove prototype message from tutorial

(this is done on the release branch in https://github.com/pytorch/audio/issues/2457)

Pull Request resolved: https://github.com/pytorch/audio/pull/2459

Reviewed By: hwangjeff

Differential Revision: D36978417

Pulled By: carolineechen

fbshipit-source-id: e580c1e8475a1a0aa924d44deea3852adc332a86

examples/tutorials/asr_inference_with_ctc_decoder_tutorial.py

@@ -11,22 +11,6 @@ using CTC loss.
 
 """
 
-######################################################################
-#
-# .. note::
-#
-#    This tutorial requires torchaudio prototype features.
-#
-#    torchaudio prototype features are available on nightly builds.
-#    Please refer to https://pytorch.org/get-started/locally/
-#    for instructions.
-#
-#    The interfaces of prototype features are unstable and subject to
-#    change. Please refer to `the nightly build documentation
-#    <https://pytorch.org/audio/main/>`__ for the up-to-date
-#    API references.
-#
-
 ######################################################################
 # Overview
 # --------