refactor(display_context): simplify scheduleRedraw logic
refactor(display_context): simplify scheduleRedraw logic

This may also improve efficiency.

google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer,janelia-flyem/neuroglancer,google/neuroglancer