Revert "Fix for issue 26243 - illegal motion of assignments in instruction merging"

tests/compiler/dart2js_extra/26243_test.dart

-import 'package:expect/expect.dart';
-
-var trace = [];
-void write(String s, int a, int b) {
-  trace.add("$s $a $b");
-}
-
-void foo() {
-  var i = 0;
-  write("foo", i, i += 1);
-}
-
-void bar() {
-  var i = 0;
-  try {
-    write("bar", i, i += 1);
-  } catch (_) {}
-}
-
-void baz() {
-  var i = 0;
-  write("baz-notry", i, i += 1);
-
-  i = 0;
-  try {
-    write("baz-try", i, i += 1);
-  } catch (_) {}
-}
-
-void main() {
-  foo();
-  bar();
-  baz();
-  Expect.listEquals(['foo 0 1', 'bar 0 1', 'baz-notry 0 1', 'baz-try 0 1'],
-      trace);
-}