Cleanup: remove unrelated files not part of DeltaSpin acceleration PR

Removed files that are not related to the main PR functionality:
- .github/ISSUE_TEMPLATE/decouple_nspin_from_hcontainer_type.md (future refactoring plan)
- deps/LibComm, deps/LibRI, deps/libpaw_interface (EXX/hybrid functional submodules)
- source/source_cell/module_symmetry/run_symmetry.cpp (standalone symmetry test)

Kept: .github/workflows/test.yml (enables 17_DS_DFTU CI test, necessary for PR)

Author: dyzheng