Revert "doc: add RTD version-switch div on furo theme"

This reverts commit c33198e.

Too much specific code is needed to have the version-switch list below
the logo. Not worth the effort.

Author: xdelaruelle

doc/source/_templates/sidebar/brand.html

@@ -140,9 +140,6 @@ def get_version_release_from_git():
         'light_logo': 'modules_red.svg',
         'dark_logo': 'modules_white.svg',
     }
-    html_context = {
-        'READTHEDOCS': True,
-    }
 
 # The name of an image file (relative to this directory) to place at the top
 # of the sidebar.