we recently added -Wextra to configure.py, and this option enables
a bunch of warning options, including `-Wignored-qualifiers`. so
there is no need to enable this specific warning anymore. this change
remove ths option from both `configure.py` and the CMake building system.
Signed-off-by: Kefu Chai <kefu.chai@scylladb.com>
Closesscylladb/scylladb#17272