[Kernel] Remove code from the old type propagation.

pkg/kernel/test/uint31_pair_map_test.dart

-import 'dart:math';
-import 'package:kernel/type_propagation/canonicalizer.dart';
-import 'package:test/test.dart';
-
-Random random = new Random(12345);
-
-main() {
-  test('Uint31PairMap randomized tests', runTest);
-}
-
-runTest() {
-  const int trials = 1000;
-  const int insertions = 1000;
-  const int uniqueKeys = 900;
-  for (int trial = 0; trial < trials; ++trial) {
-    int nextValue = 1;
-    Map<Point<int>, int> trusted = <Point<int>, int>{};
-    Uint31PairMap candidate = new Uint31PairMap();
-    for (int i = 0; i < insertions; ++i) {
-      int x = random.nextInt(uniqueKeys);
-      int y = random.nextInt(uniqueKeys);
-      Point key = new Point(x, y);
-      int trustedValue = trusted[key];
-      int candidateValue = candidate.lookup(x, y);
-      expect(candidateValue, equals(trustedValue));
-      if (trustedValue == null) {
-        int newValue = nextValue++;
-        trusted[key] = newValue;
-        candidate.put(newValue);
-      }
-    }
-  }
-}