Remove the explicit setting of a pygments theme

This allows the underlying theme being used to provide the pygments
theme instead which looks better (subjectively).

docs/conf.py

@@ -75,7 +75,7 @@
 exclude_patterns = ["_build", "Thumbs.db", ".DS_Store"]
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = "sphinx"
+# pygments_style = "sphinx"
 
 # If true, `todo` and `todoList` produce output, else they produce nothing.
 todo_include_todos = False