## Summary
`ReplaceGlobalVars` was a public IR-layer API with only one in-tree C++
caller (`relax::AttachGlobalSymbol`). The mechanism used a NodeFunctor
vtable populated at static-init time by per-dialect `.cc` files in
relax and tirx, which made the IR layer logically depend on its
dialects even though the include graph did not show it.
Move the dispatch logic into the consumer as file-local mutators and
a private helper. Delete the public header, the IR-layer driver, both
per-dialect dispatch registrations, the `IRModule.replace_global_vars`
python method, and its dedicated test file. The behavior is still
covered by `tests/python/relax/test_transform_attach_global_symbol.py`
and by the pipelines that include the `AttachGlobalSymbol` pass.
Tianqi Chen
4bcf694cbf