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/CLinesOfCode.ql

@@ -10,6 +10,7 @@
  */
 
 import python
+private import LegacyPointsTo
 
-from Function f
-select f, f.getMetrics().getNumberOfLinesOfCode() as n order by n desc
+from FunctionMetrics f
+select f, f.getNumberOfLinesOfCode() as n order by n desc