docs: removed unused extension from conf.py

Author: james

docs/language/ql-training/conf.py

@@ -33,7 +33,6 @@
     'sphinx.ext.intersphinx',
     'sphinx.ext.mathjax',
     'hieroglyph',
-    'sphinxcontrib.blockdiag',
     'sphinx.ext.graphviz',
 ]