build: Remove unused mermaid dependency

Author: sarina

requirements/base.in

@@ -7,7 +7,6 @@ sphinxcontrib-youtube
 sphinx-autobuild
 sphinx-design
 sphinx-copybutton
-sphinxcontrib-mermaid
 sphinxcontrib-images
 sphinxext-rediraffe
 sphinx-tags

source/conf.py

@@ -44,7 +44,6 @@
     "sphinx_design",
     "sphinx_copybutton",
     "sphinx.ext.graphviz",
-    "sphinxcontrib.mermaid",
     "sphinx.ext.intersphinx",
     "sphinxext.rediraffe",
     "notfound.extension",

source/developers/how-tos/add-sphinx-docs-to-a-repo.rst

@@ -38,7 +38,6 @@ Steps
       sphinx-book-theme
       sphinx-copybutton
       sphinx-autobuild
-      sphinxcontrib-mermaid
 
 #. Add ``docs.in`` to the ``upgrade`` command in your ``Makefile``
 
@@ -63,7 +62,7 @@ Steps
 
    .. code::
 
-      sphinx-quickstart --no-batchfile --extensions sphinx_copybutton --extensions sphinx.ext.graphviz --extensions sphinxcontrib.mermaid --no-sep -a "Open edX Community" -l "en" --release latest
+      sphinx-quickstart --no-batchfile --extensions sphinx_copybutton --extensions sphinx.ext.graphviz d --no-sep -a "Open edX Community" -l "en" --release latest
 
 #. Make sure the build works.