util/glsl2spirv: Fix build with Python 3.6
ChromeOS still uses Python 3.6, but the glsl2spirv script uses module '__future__.annotations', introduced in Python 3.7. Fix the build by removing module, but otherwise preserve the type annotations. Fixes: 949c3b55 ("util/glsl2spirv: add type annotations") Acked-by:Eric Engestrom <eric@igalia.com> Part-of: <mesa/mesa!20237> (cherry picked from commit bca22a65)