When using ret-sync, we should not handle item_color_changed

[saidelike]

Indeed when using ret-sync and debugging step by step, the current line keeps changing color (becomes yellow) and the previous line as well (comes back to transparent):

[idarling][DEBUG] Sending packet: UpdateLocation(name=user, ea=5372051845, color=16775936)
[idarling][DEBUG] item_color_changed() not implemented yet
[idarling][DEBUG] item_color_changed() not implemented yet

[saidelike]

We can detect if ret-sync is installed by checking for the presence of SyncPlugin.py:

        if ida_loader.find_plugin("SyncPlugin"):

but not sure how to detect if it is currently being used during a debugging session, etc.