Use errno symbols from standard library

errno symbols in sphinx.util.osutil are deprecated since Sphinx 2.0 and
have been removed in Sphinx 4.0.

Signed-off-by: Stefan Wiehler <stefan.wiehler@missinglinkelectronics.com>

sphinxcontrib/inkscapeconverter.py

@@ -17,7 +17,7 @@
 from sphinx.locale import __
 from sphinx.transforms.post_transforms.images import ImageConverter
 from sphinx.util import logging
-from sphinx.util.osutil import ENOENT, EPIPE, EINVAL
+from errno import ENOENT, EPIPE, EINVAL
 
 if False:
     # For type annotation

sphinxcontrib/rsvgconverter.py

@@ -16,7 +16,7 @@
 from sphinx.locale import __
 from sphinx.transforms.post_transforms.images import ImageConverter
 from sphinx.util import logging
-from sphinx.util.osutil import ENOENT, EPIPE, EINVAL
+from errno import ENOENT, EPIPE, EINVAL
 
 if False:
     # For type annotation