refactor(dftu): phase 6 - remove redundant dftu_io.cpp

dftu_io.cpp only contained inline JacobiRotate/CalculateEigenvalues
helpers, which are already duplicated as inline functions in
dftu_base.cpp (where write_occup_m uses them). The file had no
non-inline symbols, so deleting it is safe.

- git rm source_lcao/module_dftu/dftu_io.cpp
- source_lcao/module_dftu/CMakeLists.txt: remove dftu_io.cpp from dftu
  OBJECT library
- Makefile.Objects: remove dftu_io.o from OBJS_DFTU

Verified: make -j 30 in build_max_para_test succeeds; all dftu unit
tests pass (dftu_core_test: 10, dftu_pw_test: 11, dftu_operator_test:
15, MODULE_LCAO_operator_dftu_test: 2).

Author: abacus_fixer

source/Makefile.Objects

@@ -811,7 +811,6 @@ OBJS_DFTU=dftu.o\
       dftu_force.o\
       dftu_yukawa.o\
       dftu_folding.o\
-      dftu_io.o\
       dftu_tools.o\
       dftu_occup.o\
       dftu_hamilt.o\

source/source_lcao/module_dftu/CMakeLists.txt

@@ -3,7 +3,6 @@ list(APPEND objects
       dftu_force.cpp
       dftu_yukawa.cpp
       dftu_folding.cpp
-      dftu_io.cpp
       dftu_tools.cpp
       dftu_occup.cpp
       dftu_hamilt.cpp