fix(docs): bump up sphinx version

Set the minimum version of sphinx required to 5.3.0 and pin the
version for all the packages mentioned in requirements.txt. This is
done to resolve read-the-docs build error which needs this version
of sphinx. Also removed dependency on some unneeded python packages.

Signed-off-by: Arunachalam Ganapathy <arunachalam.ganapathy@arm.com>
Change-Id: I0638d0df20017b85d9d7c1672e848ba5d3f25c48
diff --git a/docs/conf.py b/docs/conf.py
index 6022a79..f97f476 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -34,7 +34,7 @@
 # Add any Sphinx extension module names here, as strings. They can be
 # extensions coming with Sphinx (named 'sphinx.ext.*') or your custom
 # ones.
-extensions = ['sphinx.ext.autosectionlabel', 'sphinxcontrib.plantuml']
+extensions = ['sphinx.ext.autosectionlabel']
 
 # Add any paths that contain templates here, relative to this directory.
 templates_path = ['_templates']
@@ -59,7 +59,7 @@
   rst_prolog = subs.read()
 
 # Minimum version of sphinx required
-needs_sphinx = '2.4'
+needs_sphinx = '5.3.0'
 
 # -- Options for HTML output -------------------------------------------------