Clean ASR older and non-maintained models and its respective modules

[nithinraok]

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What does this PR do ?

Remove deprecated and unmaintained ASR model architectures

Collection: ASR

Changelog

• Remove QuartzNet model, configs, pretrained model entries, and related tests
• Remove Squeezeformer encoder, modules, configs, pretrained model entries, and tests
• Remove ContextNet configs and pretrained model entries
• Remove CitriNet configs, SSL configs, and pretrained model entries
• Remove MSDD Diarizer models and related tests
• Remove SLU models and related tests
• Remove examples/asr/experimental/ directory
• Remove K2 model classes (EncDecK2RnntSeqModelBPE, k2 aligner, graph compilers/decoders, lattice losses, etc.), keeping only core K2 loss/utility code (graph_transducer.py, rnnt_logprobs.py, rnnt_logprobs_triton.py, w_transducer.py)
• Replace QuartzNet references in remaining tests with supported models (e.g., FastConformer)

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• Related to # (issue)

[tango4j]

I have checked and fixed the deprecated MSDD-related codes and documents.
Also, updated diarization documents with the latest Sortformer models on HF.
I asked @ipmedenn to double check if there is any issues or critical missing part.
But I think if test passes, speaker diarization part is good to go.

[artbataev]

LGTM. All changes look reasonable.
Please fix failing tests.
Special thanks for removing old k2-related code!

[nithinraok]

Two failed tests are fixed on main. So merging this PR>