docs: rename ql-training-rst > ql-training

docs/language/ql-training/query-examples/cpp/control-flow-cpp-3.ql

@@ -0,0 +1,10 @@
+import cpp
+
+from LocalVariable lv, ControlFlowNode def
+where
+  def = lv.getAnAssignment() and
+  not exists(VariableAccess use |
+    use = lv.getAnAccess() and
+    use = def.getASuccessor+()
+  )
+select lv, def