Remove references to previously-vendored Sphinx extensions (pandas-de…

…v#46624)

LICENSES/OTHER

@@ -1,8 +1,3 @@
-numpydoc license
-----------------
-
-The numpydoc license is in pandas/doc/sphinxext/LICENSE.txt
-
 Bottleneck license
 ------------------
 
@@ -77,4 +72,4 @@ DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
-SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

doc/sphinxext/README.rst

@@ -1,17 +1,5 @@
 sphinxext
 =========
 
-This directory contains copies of different sphinx extensions in use in the
-pandas documentation. These copies originate from other projects:
-
-- ``numpydoc`` - Numpy's Sphinx extensions: this can be found at its own
-  repository: https://github.com/numpy/numpydoc
-- ``ipython_directive`` and ``ipython_console_highlighting`` in the folder
-  ``ipython_sphinxext`` - Sphinx extensions from IPython: these are included
-  in IPython: https://github.com/ipython/ipython/tree/master/IPython/sphinxext
-
-.. note::
-
-    These copies are maintained at the respective projects, so fixes should,
-    to the extent possible, be pushed upstream instead of only adapting our
-    local copy to avoid divergence between the local and upstream version.
+This directory contains custom sphinx extensions in use in the pandas
+documentation.