Fix three tests failing with GMT dev version (#970)

- Refactored test_basemap_winkel_tripel and test_plot_projection to use `@check_figures_equal()`. 
- Removed test_basemap_aliases which wasn't a good test. 
- Removed the baseline images since not needed anymore.

Author: weiji14

pygmt/tests/baseline/test_basemap_aliases.png

@@ -77,24 +77,15 @@ def test_basemap_polar():
     return fig_ref, fig_test
 
 
-@pytest.mark.mpl_image_compare
+@check_figures_equal()
 def test_basemap_winkel_tripel():
     """
     Create a Winkel Tripel basemap plot.
     """
-    fig = Figure()
-    fig.basemap(R="90/450/-90/90", J="R270/25c", B="afg")
-    return fig
-
-
-@pytest.mark.mpl_image_compare
-def test_basemap_aliases():
-    """
-    Make sure the argument aliases work.
-    """
-    fig = Figure()
-    fig.basemap(region=[0, 360, -90, 90], projection="W7i", frame=True)
-    return fig
+    fig_ref, fig_test = Figure(), Figure()
+    fig_ref.basemap(R="90/450/-90/90", J="R270/25c", B="afg")
+    fig_test.basemap(region=[90, 450, -90, 90], projection="R270/25c", frame="afg")
+    return fig_ref, fig_test
 
 
 @check_figures_equal()

pygmt/tests/baseline/test_basemap_winkel_tripel.png

@@ -119,13 +119,21 @@ def test_plot_fail_size_color(data):
         )
 
 
-@pytest.mark.mpl_image_compare
+@check_figures_equal()
 def test_plot_projection(data):
     """
     Plot the data in green squares with a projection.
     """
-    fig = Figure()
-    fig.plot(
+    fig_ref, fig_test = Figure(), Figure()
+    fig_ref.plot(
+        data=POINTS_DATA,
+        R="g",
+        J="R270/4i",
+        S="s0.2c",
+        G="green",
+        B="ag",
+    )
+    fig_test.plot(
         x=data[:, 0],
         y=data[:, 1],
         region="g",
@@ -134,7 +142,7 @@ def test_plot_projection(data):
         color="green",
         frame="ag",
     )
-    return fig
+    return fig_ref, fig_test
 
 
 @check_figures_equal()