Disable backup/restore stress test (#7350)

Summary:
Seems it's causing some tests failures.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/7350

Reviewed By: riversand963

Differential Revision: D23544109

Pulled By: jay-zhuang

fbshipit-source-id: 798a0ca374a20b6c2d0f29582729ff101c6a2e99

tools/db_crashtest.py

@@ -29,9 +29,6 @@ expected_values_file = tempfile.NamedTemporaryFile()
 
 default_params = {
     "acquire_snapshot_one_in": 10000,
-    "backup_max_size": 100 * 1024 * 1024,
-    # Consider larger number when backups considered more stable
-    "backup_one_in": 100000,
     "block_size": 16384,
     "bloom_bits": lambda: random.choice([random.randint(0,19),
                                          random.lognormvariate(2.3, 1.3)]),