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/test/library-tests/ControlFlow/general/Lines.ql

@@ -1,8 +1,9 @@
 import python
+private import LegacyPointsTo
 
 from Scope s, int n
 where
-  exists(Function f | f = s | n = f.getMetrics().getNumberOfLines())
+  exists(FunctionMetrics f | f = s | n = f.getNumberOfLines())
   or
-  exists(Module m | m = s | n = m.getMetrics().getNumberOfLines())
+  exists(ModuleMetrics m | m = s | n = m.getNumberOfLines())
 select s.toString(), n