[doc] Use native numfig extension

doc/conf.py

@@ -55,12 +55,14 @@ extensions = [
     'sphinx.ext.graphviz',
     'sphinx.ext.napoleon',
     'sphinx.ext.viewcode',
-    'sphinx_numfig',
     ]
 
 # Always includes todos
 todo_include_todos = True
 
+# Create numbers on figures with captions
+numfig = True
+
 # Generates auto-summary automatically
 autosummary_generate = True
 

setup.py

@@ -59,7 +59,6 @@ setup(
       "simplejson",
       "six",
       "sphinx",
-      "sphinx-numfig",
       "pyzmq",
     ],