Is the --spirv-debug-info-version=ocl-100 needed for debugging.

[diptorupd]

@akharche @reazulhoque The "--spirv-debug-info-version=ocl-100" in spirv_generator.generate is not used in any place. Is the flag essential for us to support GDB? If not the dead code should removed.

Originally posted by @diptorupd in https://github.com/IntelPython/numba-dppy/pull/481#r658251601

[akharche]

The flag is not essential in GDB supporting, it just fixes 1 error in spirv-validation. The flag is used again here: https://github.com/IntelPython/numba-dppy/pull/412