Move `set_title` outside of `snapshot`

In some use cases, we would rather not overwrite the title. For
example, if we overlap eddies at several dates, we may want to keep
the first date. Argument k was only used for the title. It is also
clearer not to have k as an argument because it did not select the
eddies plotted, the selection is made by argument `ishape_list`.

Analysis/plot_eddy_contours.py

@@ -54,14 +54,12 @@ def select_ishapes(k, k1, ishape_last, reader_extr, window = None):
 
     return ishape_list
 
-def snapshot(k, ax, ishape_list, reader_extr, reader_outer, reader_m_s = None,
-             *, dashed = False, light = False, src_crs = ccrs.PlateCarree()):
+def snapshot(ax, ishape_list, reader_extr, reader_outer, reader_m_s = None, *,
+             dashed = False, light = False, src_crs = ccrs.PlateCarree()):
     """Plots extrema, outermost contours and max-speed contours.
 
     dashed: boolean."""
     
-    ax.set_title(f"k = {k}", y = 1.05)
-    
     for ishape in ishape_list:
         shape_rec_extr = reader_extr.shapeRecord(ishape)
         shape_outer = reader_outer.shape(ishape)
@@ -277,7 +275,8 @@ if __name__ == "__main__":
         if args.window is None: plot_grid_bb(args.shp_tr_dir, ax)
         ishape_list = select_ishapes(k, k1, ishape_last, reader_extr,
                                      args.window)
-        snapshot(k, ax, ishape_list, reader_extr, reader_outer, reader_m_s,
+        ax.set_title(f"k = {k}", y = 1.05)
+        snapshot(ax, ishape_list, reader_extr, reader_outer, reader_m_s,
                  dashed = args.dashed, light = args.light)
         ax.gridlines(draw_labels = True)
         ax.coastlines()