doc: drop intersphinx mapping

In practice it's used only for the python base types (int, str, bool,
etc), which isn't particularly helpful. On the other hand, it causes
complains during package build during manpage generation, as it's done
offline, and may also cause reproducibility issues.

doc/conf.py

@@ -406,10 +406,3 @@
 # If true, do not generate a @detailmenu in the "Top" node's menu.
 #
 # texinfo_no_detailmenu = False
-
-
-# Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {
-    'python': ('https://docs.python.org/', None),
-    'qubes': ('https://dev.qubes-os.org/projects/qubes-core-admin/en/latest', None),
-}