Remove DSP feature tutorials (#3985)

Co-authored-by: Sam Anklesaria <[email protected]>

Author: samanklesaria

docs/source/index.rst

@@ -213,34 +213,6 @@ Tutorials
    :link: tutorials/audio_feature_augmentation_tutorial.html
    :tags: Preprocessing
 
-.. customcarditem::
-   :header: Generating waveforms with oscillator
-   :card_description:
-   :image: _images/sphx_glr_oscillator_tutorial_003.png
-   :link: tutorials/oscillator_tutorial.html
-   :tags: DSP
-
-.. customcarditem::
-   :header: Additive Synthesis
-   :card_description:
-   :image: _images/sphx_glr_additive_synthesis_tutorial_001.png
-   :link: tutorials/additive_synthesis_tutorial.html
-   :tags: DSP
-
-.. customcarditem::
-   :header: Designing digital filters
-   :card_description:
-   :image: _images/sphx_glr_filter_design_tutorial_001.png
-   :link: tutorials/filter_design_tutorial.html
-   :tags: DSP
-
-.. customcarditem::
-   :header: Subtractive Synthesis
-   :card_description:
-   :image: _images/sphx_glr_subtractive_synthesis_tutorial_002.png
-   :link: tutorials/subtractive_synthesis_tutorial.html
-   :tags: DSP
-
 .. customcarditem::
    :header: Audio dataset
    :card_description: Learn how to use <code>torchaudio.datasets</code> module.