[refactor] [opengl] Get rid of some no-ops in linear seek
[refactor] [opengl] Get rid of some no-ops in linear seek

Reduced p2g shader from 658 lines to 514 lines.

ghstack-source-id: 67fcba2489eda606d334336a98af083b35b74df1
Pull Request resolved: https://github.com/taichi-dev/taichi/pull/3980
yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi,yuanming-hu/taichi