Remove unused data types (ROW_REF_DATA and ROW_REF_VECTOR_DATA).
Remove an old comment.
Add -Wextra to CXXFLAGS.
Remove an unused argument.
Suppress warnings for unused arguments in column.cpp.
Suppress warnings for unused arguments in table.cpp.
Suppress warnings for unused arguments in sorter.cpp.
Suppress warnings for unused arguments in pipeline.cpp.
Suppress warnings for unused arguments in db.cpp.
Suppress warnings for unused arguments in index.cpp.
Suppress warnings for unused arguments in expression.cpp.