Revert plotting across dateline workarounds (#585)

Remove workarounds added because plotting grids
across the dateline would crash, not needed since
bumping minimum required GMT version to 6.1.1.

* Revert runfirst workaround for test_grdimage_over_dateline
* Revert grdtrack example workaround in #531 crashing due to bad meridian
* Remove unneeded pytest mpl_image_compare and runfirst markers

Makefile

@@ -29,11 +29,7 @@ test:
 	@echo ""
 	@cd $(TESTDIR); python -c "import $(PROJECT); $(PROJECT).show_versions()"
 	@echo ""
-	# There are two steps to the test here because `test_grdimage_over_dateline`
-	# passes only when it runs before the other tests.
-	# See also https://github.com/GenericMappingTools/pygmt/pull/476
-	cd $(TESTDIR); pytest -m runfirst $(PYTEST_ARGS) $(PROJECT)
-	cd $(TESTDIR); pytest -m 'not runfirst' $(PYTEST_ARGS) $(PROJECT)
+	cd $(TESTDIR); pytest $(PYTEST_ARGS) $(PROJECT)
 	cp $(TESTDIR)/coverage.xml .
 	cp -r $(TESTDIR)/htmlcov .
 	rm -r $(TESTDIR)

examples/gallery/grid/track_sampling.py

@@ -24,7 +24,7 @@
 
 fig = pygmt.Figure()
 # Plot the earth relief grid on Cylindrical Stereographic projection, masking land areas
-fig.basemap(region="d", frame=True, projection="Cyl_stere/8i")
+fig.basemap(region="g", frame=True, projection="Cyl_stere/150/-20/8i")
 fig.grdimage(grid=grid, cmap="gray")
 fig.coast(land="#666666")
 # Plot using circles (c) of 0.15cm, the sampled bathymetry points

pygmt/tests/test_grdimage.py

@@ -76,10 +76,6 @@ def test_grdimage_fails():
         fig.grdimage(np.arange(20).reshape((4, 5)))
 
 
-# This test needs to run first before the other tests (on Linux at least) so
-# that a black image isn't plotted due to an `inf` value when resampling.
-# See also https://github.com/GenericMappingTools/pygmt/pull/476
-@pytest.mark.runfirst
 @pytest.mark.mpl_image_compare
 def test_grdimage_over_dateline(xrgrid):
     """

setup.cfg

@@ -12,8 +12,3 @@ max-line-length = 88
 max-doc-length = 79
 exclude =
     pygmt/_version.py
-
-[tool:pytest]
-markers =
-    mpl_image_compare: compare generated plots with correct baseline version
-    runfirst: runs the test(s) first before the other ones