test: ssh: update mock version to 3.0.0 min

tests/requirements.txt

@@ -4,7 +4,7 @@ pytest-cov>=2.6.1
 pytest-xdist>=1.26.1
 pytest-mock>=1.10.4
 flaky>=3.5.3
-mock>=2.0.0
+mock>=3.0.0
 xmltodict>=0.11.0
 awscli>=1.16.125
 google-compute-engine

tests/unit/remote/ssh/test_ssh.py

@@ -4,8 +4,7 @@ import sys
 
 from unittest import TestCase
 
-import mock
-from mock import patch
+from mock import patch, mock_open
 import pytest
 
 from dvc.remote.ssh import RemoteSSH
@@ -54,24 +53,6 @@ Host example.com
    IdentityFile ~/.ssh/not_default.key
 """
 
-# compat version for mock library version 2
-# mock 2.0.0 can't iterate in mock_open
-if mock.version_info[0] < 3:
-
-    def mock_open_compat(*args, **kargs):
-        f_open = mock.mock_open(*args, **kargs)
-        if sys.version_info.major == 3:
-            f_open.return_value.__iter__ = lambda self: self
-            f_open.return_value.__next__ = lambda self: self.readline()
-        else:
-            f_open.return_value.__iter__ = lambda self: iter(self.readline, "")
-
-        return f_open
-
-    mock_open = mock_open_compat
-else:
-    mock_open = mock.mock_open
-
 if sys.version_info.major == 3:
     builtin_module_name = "builtins"
 else: