Remove deprecated mamba2 model configs

[ananthsub]

What does this PR do ?

These configs were marked as deprecated in the 0.2.0 release (25.11 container) and will be removed as part of the next release. Newer hybrid model configs supersede these.

Changelog

• Remove historical, experimental Mamba2 model provider configs & recipes

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[ananthsub]

/ok to test c6c0581

[ananthsub]

/ok to test 8a3302e