deltaspin: remove redundant sc_parse_json.cpp

sc_parse_json.cpp contained only two explicit template instantiations
(template class spinconstrain::SpinConstrain<std::complex<double>> and
the double specialization) at global scope. The same instantiations
already exist at the end of spin_constrain.cpp (inside namespace
spinconstrain, lines 733-734), making this file dead code.

History: the file predates the instantiations being added to
spin_constrain.cpp; once those landed, sc_parse_json.cpp became
redundant but was never cleaned up. The misleading filename (suggests
JSON parsing) is also retired.

Verification: cmake --build build_std_para --target deltaspin -j4
built successfully; SpinConstrain<TK> symbols still resolve via the
in-file instantiations in spin_constrain.cpp.

Author: abacus_fixer

source/source_lcao/module_deltaspin/CMakeLists.txt

@@ -8,7 +8,6 @@ list(APPEND objects
     cal_mw_from_lambda.cpp
     template_helpers.cpp
     deltaspin_lcao.cpp
-    sc_parse_json.cpp
     cal_mw_helper.cpp
     mi_tools.cpp
 )