Python: Fix all metrics-related compilation failures

In hindsight, having a `.getMetrics()` method that just returns `this`
is somewhat weird. It's possible that it predates the existence of the
inline cast, however.

python/ql/src/Metrics/FunctionStatementNestingDepth.ql

@@ -11,6 +11,7 @@
  */
 
 import python
+private import LegacyPointsTo
 
 from FunctionMetrics func
 select func, func.getStatementNestingDepth() as n order by n desc