Remove `ymm` embedded rounding code in JIT and AVX10 APIs

[anthonycanino]

AVX10 will no longer have an associated 256-bit only implementation. As part of that revision, ymm embedded rounding as a potential feature will no longer be implemented as a hardware feature. This task is to go through and remove the code associated with the feature in the JIT and the public APIs that allow for embedded rounding on a 256-bit ymm lowering.

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[tannergooding]

This work was completed in #115235