Clean up unnecessary script tags

Many tests loaded desktop-gl-constants.js even though they do not need
it. Clean up these.
Merge pull request #411 from NVIDIA/script-tag-cleanup

Clean up unnecessary script tags
Update two tests.
Merge pull request #412 from baxissimo/fix-accuracy-conf-tests

Update two tests that were being more aggressive than the ES GLSL 1.0 spec actually guarantees.