Drop failing tests writing multi-dimensional arrays as attributes (#2810)

These aren't valid for netCDF files.

Fixes GH2803

Author: shoyer

xarray/tests/test_backends.py

@@ -3444,11 +3444,6 @@ def new_dataset_and_coord_attrs():
             with create_tmp_file() as tmp_file:
                 ds.to_netcdf(tmp_file)
 
-            ds, attrs = new_dataset_and_attrs()
-            attrs['test'] = np.arange(12).reshape(3, 4)
-            with create_tmp_file() as tmp_file:
-                ds.to_netcdf(tmp_file)
-
             ds, attrs = new_dataset_and_attrs()
             attrs['test'] = 'This is a string'
             with create_tmp_file() as tmp_file:
@@ -3459,11 +3454,6 @@ def new_dataset_and_coord_attrs():
             with create_tmp_file() as tmp_file:
                 ds.to_netcdf(tmp_file)
 
-            ds, attrs = new_dataset_and_attrs()
-            attrs['test'] = np.arange(12).reshape(3, 4)
-            with create_tmp_file() as tmp_file:
-                ds.to_netcdf(tmp_file)
-
 
 @requires_scipy_or_netCDF4
 class TestDataArrayToNetCDF(object):