Python: Get rid of getLiteralValue

This had only two uses in our libraries, so I simply inlined the
predicate body in both places.

python/ql/lib/semmle/python/Exprs.qll

@@ -337,8 +337,6 @@ abstract class ImmutableLiteral extends Expr {
   abstract Object getLiteralObject();
 
   abstract boolean booleanValue();
-
-  final Value getLiteralValue() { result.(ConstantObjectInternal).getLiteral() = this }
 }
 
 /** A numerical constant expression, such as `7` or `4.2` */

python/ql/src/Expressions/IsComparisons.qll

@@ -2,6 +2,7 @@
 
 import python
 private import LegacyPointsTo
+private import semmle.python.objects.ObjectInternal
 
 /** 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) {
@@ -121,7 +122,7 @@ predicate invalid_portable_is_comparison(Compare comp, Cmpop op, ClassValue cls)
   // OK to use 'is' when comparing items from a known set of objects
   not exists(Expr left, Expr right, Value val |
     comp.compares(left, op, right) and
-    exists(ImmutableLiteral il | il.getLiteralValue() = val)
+    exists(ImmutableLiteral il | il = val.(ConstantObjectInternal).getLiteral())
   |
     left.pointsTo(val) and right.pointsTo(val)
     or

python/ql/src/Expressions/WrongNumberArgumentsForFormat.ql

@@ -14,6 +14,7 @@
  */
 
 import python
+import semmle.python.objects.ObjectInternal
 import semmle.python.strings
 
 predicate string_format(BinaryExpr operation, StringLiteral str, Value args, AstNode origin) {
@@ -31,7 +32,7 @@ int sequence_length(Value args) {
     not seq.getAnElt() instanceof Starred
   )
   or
-  exists(ImmutableLiteral i | i.getLiteralValue() = args | result = 1)
+  exists(ImmutableLiteral i | i = args.(ConstantObjectInternal).getLiteral() | result = 1)
 }
 
 from