Emscripten: remove support for `-sWASM_BIGINT=0` (#874) * Emscripten: cleanup * Emscripten: remove support for `-sWASM_BIGINT=0` * Emscripten: remove redundant CircleCI config * Emscripten: modernize CI * Ensure test helper methods are static Similar to #644. * Fix test failures in `cls_multi_{s,u}shortchar`