chore: remove deprecated mcp-types crate (#10357)

https://github.com/openai/codex/pull/10349 migrated us off of
`mcp-types`, so this PR deletes the code.

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[//]: # (BEGIN SAPLING FOOTER)
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* __->__ #10357
* #10349
* #10356

.github/workflows/rust-ci.yml

@@ -64,8 +64,6 @@ jobs:
           components: rustfmt
       - name: cargo fmt
         run: cargo fmt -- --config imports_granularity=Item --check
-      - name: Verify codegen for mcp-types
-        run: ./mcp-types/check_lib_rs.py
 
   cargo_shear:
     name: cargo shear