[poincare] Fix extractUnit into removeUnit paradigm

poincare/src/expression.cpp

@@ -350,7 +350,9 @@ Expression Expression::defaultHandleUnitsInChildren() {
   // Generically, an Expression does not accept any Unit in its children.
   const int childrenCount = numberOfChildren();
   for (int i = 0; i < childrenCount; i++) {
-    if (!childAtIndex(i).extractUnits().isUninitialized()) {
+    Expression unit;
+    childAtIndex(i).removeUnit(&unit);
+    if (!unit.isUninitialized()) {
       return replaceWithUndefinedInPlace();
     }
   }