Remove unused option annual_mean_kwargs from all recipes (#4133)

Author: schlunma

esmvaltool/recipes/ref/recipe_ref_annual_cycle_region.yml

@@ -113,7 +113,6 @@ diagnostics:
         group_variables_by: variable_group
         plots:
           annual_cycle:
-            annual_mean_kwargs: False
             plot_kwargs:
               default:
                 color: red

esmvaltool/recipes/ref/recipe_ref_timeseries_region.yml

@@ -161,7 +161,6 @@ diagnostics:
         group_variables_by: variable_group
         plots:
           timeseries:
-            annual_mean_kwargs: False
             plot_kwargs:
               default:
                 color: red
@@ -247,7 +246,6 @@ diagnostics:
         group_variables_by: variable_group
         plots:
           timeseries:
-            annual_mean_kwargs: False
             plot_kwargs:
               default:
                 color: red