Provisionally stop working around issues 9252 and 9253.

utils/pub/system_cache.dart

Index: utils/pub/system_cache.dart
diff --git a/utils/pub/system_cache.dart b/utils/pub/system_cache.dart
index e93f8f4f56d07c09971f1ae6d15d976321e02d97..b6467b5f88f78f12aa18e4928c1ea1fce2ec7007 100644
--- a/utils/pub/system_cache.dart
+++ b/utils/pub/system_cache.dart
@@ -108,12 +108,10 @@ class SystemCache {
     return io.createTempDir(path.join(temp, 'dir'));
   }
 
-  /// Delete's the system cache's internal temp directory.
-  Future deleteTempDir() {
+  /// Deletes the system cache's internal temp directory.
+  void deleteTempDir() {
     log.fine('Clean up system cache temp directory $tempDir.');
-    return defer(() {
-      if (!dirExists(tempDir)) return;
-      return deleteDir(tempDir);
-    });
+    if (!dirExists(tempDir)) return;
+    deleteDir(tempDir);
   }
 }