Nested axes in output of recipe_martin18_grl and recipe_li17natcc

[lukruh]

The two recipes recipe_martin18grl and recipe_li17natcc.yml produce figures where additional frames (nested axis) are shown (example).

For recipe_martin18grl they are probably created here (and L561):

ESMValTool/esmvaltool/diag_scripts/droughtindex/collect_drought_func.py

Lines 465 to 467 in e01d7b7

	fig, axx = plt.subplots(figsize=(8, 4))
	axx = plt.axes(projection=cart.PlateCarree(central_longitude=0.0))

and for recipe_li17natcc.yml :

ESMValTool/esmvaltool/diag_scripts/emergent_constraints/lif1f2.py

Line 143 in e01d7b7

axx = plt.axes(projection=cart.PlateCarree())