Don't migrate status entries under a "[ $strong ]" header.

tools/migration/lib/src/migrate_statuses.dart

Index: tools/migration/lib/src/migrate_statuses.dart
diff --git a/tools/migration/lib/src/migrate_statuses.dart b/tools/migration/lib/src/migrate_statuses.dart
index 900cc0284ccbeb5010718ce52df82e7a2f142ef6..36c2606be459b544872ec17490603ac99ec4bb96 100644
--- a/tools/migration/lib/src/migrate_statuses.dart
+++ b/tools/migration/lib/src/migrate_statuses.dart
@@ -107,6 +107,12 @@ class EntrySet {
       return false;
     }
 
+    // The main "_strong.status" files skip lots of tests that are or were not
+    // strong mode clean. We don't want to skip those tests in 2.0 -- we want
+    // to fix them. If we're in that header, do remove the entry from the old
+    // file, but don't add it to the new one.
+    if (header == "[ \$strong ]") return true;
+
     // If the condition places it directly into one file, put it there.
     if (possibleFiles.length == 1) {
       destination = "${toDir}_${possibleFiles.single}.status";