Remove xfails on grdimage test for GMT 6.2.0rc2 (#1296)

Since `test_grdimage_shading_xarray` runs properly in GMT
6.2.0, the expected failure (xfail) marker can be removed.

Author: weiji14

pygmt/tests/test_grdimage.py

@@ -1,20 +1,14 @@
 """
 Test Figure.grdimage.
 """
-import sys
-
 import numpy as np
 import pytest
 import xarray as xr
-from packaging.version import Version
-from pygmt import Figure, clib
+from pygmt import Figure
 from pygmt.datasets import load_earth_relief
 from pygmt.exceptions import GMTInvalidInput
 from pygmt.helpers.testing import check_figures_equal
 
-with clib.Session() as _lib:
-    gmt_version = Version(_lib.info["version"])
-
 
 @pytest.fixture(scope="module", name="grid")
 def fixture_grid():
@@ -82,14 +76,6 @@ def test_grdimage_file():
     return fig
 
 
-@pytest.mark.skipif(
-    gmt_version <= Version("6.1.1") and sys.platform == "darwin",
-    reason="Upstream bug in GMT 6.1.1 that causes segfault on macOS",
-)
-@pytest.mark.xfail(
-    condition=gmt_version <= Version("6.1.1") and sys.platform != "darwin",
-    reason="Upstream bug in GMT 6.1.1 that causes this test to fail on Linux/Windows",
-)
 @check_figures_equal()
 @pytest.mark.parametrize(
     "shading",