DOC: removed vendored IPython.sphinxext - take 2 (#19657)

Author: jorisvandenbossche

ci/requirements-optional-conda.txt

@@ -4,7 +4,7 @@ bottleneck
 fastparquet
 feather-format
 html5lib
-ipython
+ipython>=5.6.0
 ipykernel
 jinja2
 lxml

ci/requirements-optional-pip.txt

@@ -6,7 +6,7 @@ bottleneck
 fastparquet
 feather-format
 html5lib
-ipython
+ipython>=5.6.0
 ipykernel
 jinja2
 lxml

doc/source/conf.py

@@ -64,9 +64,7 @@
               'sphinx.ext.extlinks',
               'sphinx.ext.todo',
               'numpydoc',
-              'ipython_sphinxext.ipython_directive',
-              'ipython_sphinxext.ipython_console_highlighting',
-              # lowercase didn't work
+              'IPython.sphinxext.ipython_directive',
               'IPython.sphinxext.ipython_console_highlighting',
               'matplotlib.sphinxext.plot_directive',
               'sphinx.ext.intersphinx',