Python: Fix query tests

Mostly just adding `private import LegacyPointsTo`. Sometimes getting
rid of other imports that are superceded by that module.

python/ql/src/Metrics/Dependencies/ExternalDependenciesSourceLinks.ql

@@ -8,6 +8,7 @@
 
 import python
 import semmle.python.dependencies.TechInventory
+private import LegacyPointsTo
 
 /*
  * This query creates the source links for the ExternalDependencies.ql query.

python/ql/src/Metrics/DirectImports.ql

@@ -11,6 +11,7 @@
  */
 
 import python
+private import LegacyPointsTo
 
 from ModuleValue m, int n
 where n = count(ModuleValue imp | imp = m.getAnImportedModule())

python/ql/src/Metrics/TransitiveImports.ql

@@ -11,6 +11,7 @@
  */
 
 import python
+private import LegacyPointsTo
 
 from ModuleValue m, int n
 where n = count(ModuleValue imp | imp = m.getAnImportedModule+() and imp != m)