Python: Remove points-to references from python.qll

For now, these have just been made into `private` imports. After doing
this, I went through all of the (now not compiling) files and added in
private imports to the modules that they actually depended on.

I also added an explicit import of `LegacyPointsTo` (even though it may
be unnecessary) in cases where the points-to dependency was somewhat
surprising (and one we want to get rid of). This was primarily inside
the various SSA layers.

For modules inside `semmle.python.{types, objects, pointsto}` I did not
bother, as these are fairly clearly related to points-to.

python/ql/src/Expressions/ContainsNonContainer.ql

@@ -13,7 +13,6 @@
 
 import python
 private import LegacyPointsTo
-import semmle.python.pointsto.PointsTo
 
 predicate rhs_in_expr(ControlFlowNode rhs, Compare cmp) {
   exists(Cmpop op, int i | cmp.getOp(i) = op and cmp.getComparator(i) = rhs.getNode() |

python/ql/src/Expressions/IsComparisons.qll

@@ -3,6 +3,7 @@
 import python
 private import LegacyPointsTo
 private import semmle.python.objects.ObjectInternal
+private import semmle.python.objects.ObjectAPI
 
 /** Holds if the comparison `comp` uses `is` or `is not` (represented as `op`) to compare its `left` and `right` arguments. */
 predicate comparison_using_is(Compare comp, ControlFlowNode left, Cmpop op, ControlFlowNode right) {

python/ql/src/Statements/RedundantAssignment.ql

@@ -14,6 +14,7 @@
 
 import python
 private import LegacyPointsTo
+private import semmle.python.objects.ObjectAPI
 
 predicate assignment(AssignStmt a, Expr left, Expr right) {
   a.getATarget() = left and a.getValue() = right

python/ql/src/Variables/UndefinedGlobal.ql

@@ -14,7 +14,6 @@ import python
 private import LegacyPointsTo
 import Variables.MonkeyPatched
 import Loop
-import semmle.python.pointsto.PointsTo
 
 predicate guarded_against_name_error(Name u) {
   exists(Try t | t.getBody().getAnItem().contains(u) |

python/ql/src/Variables/UninitializedLocal.ql

@@ -14,7 +14,6 @@
 import python
 private import LegacyPointsTo
 import Undefined
-import semmle.python.pointsto.PointsTo
 
 predicate uninitialized_local(NameNode use) {
   exists(FastLocalVariable local | use.uses(local) or use.deletes(local) |

python/ql/src/analysis/Efficiency.ql

@@ -5,8 +5,6 @@
 
 import python
 private import LegacyPointsTo
-import semmle.python.pointsto.PointsTo
-import semmle.python.pointsto.PointsToContext
 
 predicate trivial(ControlFlowNode f) {
   f.getNode() instanceof Parameter