Remove unused batched-LDE wrapper functions

[MauroToscano]

Pure deletion of dead code — −75 lines, 0 added.

These three pub fns in crypto/math-cuda/src/lde.rs have no callers anywhere (verified across the whole repo — the only references are their own definitions and an assert_u32_domain message string):

• coset_lde_batch_base_into_with_merkle_tree
• coset_lde_batch_ext3_into_with_merkle_tree
• coset_lde_batch_ext3_into_with_leaf_hash

They are thin non-_keep wrappers that delegate to the *_inner functions. Those *_inner functions stay alive through their other callers, so nothing is orphaned by this removal:

• ..._base_..._inner — still called by coset_lde_batch_base_into_with_merkle_tree_keep (the R1 GPU path, called from stark::gpu_lde) and coset_lde_batch_base_into_with_leaf_hash.
• ..._ext3_..._inner — still called by coset_lde_batch_ext3_into_with_merkle_tree_keep.

This is independent of #715; the functions were already dead on main (their caller count is unchanged by any open PR).

Verification

• Whole-repo grep: zero references to the three functions outside their (now-deleted) definitions.
• The *_inner helpers and both *_keep variants are retained and still referenced.
• rustfmt clean.
• Not compiled locally — math-cuda requires the CUDA toolchain (no nvcc on the dev box). This is a pure deletion of verified-uncalled functions with no remaining references, but a CUDA build should confirm before merge.