nanshe_ipython: Remove ROI trace HTML file before saving.
nanshe_ipython: Remove ROI trace HTML file before saving.

Goes ahead and removes the ROI trace plot's HTML file before saving it.
This avoids a warning about overwriting the plot. Also should avoid some
oddities with the Docker container that we have seen before mainly with
HDF5 files.

nanshe-org/nanshe_workflow,DudLab/nanshe_workflow