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/Summary/LinesOfCode.ql

@@ -10,5 +10,6 @@
  */
 
 import python
+private import LegacyPointsTo
 
-select sum(Module m | | m.getMetrics().getNumberOfLinesOfCode())
+select sum(ModuleMetrics m | | m.getNumberOfLinesOfCode())

python/ql/src/Summary/LinesOfUserCode.ql

@@ -14,10 +14,11 @@
 
 import python
 import semmle.python.filters.GeneratedCode
+private import LegacyPointsTo
 
-select sum(Module m |
+select sum(ModuleMetrics m |
     exists(m.getFile().getRelativePath()) and
     not m.getFile() instanceof GeneratedFile
   |
-    m.getMetrics().getNumberOfLinesOfCode()
+    m.getNumberOfLinesOfCode()
   )