Fix typing for Python <3.7

Fix a runtime issue with ACTS running on versions of Python less than
3.7. Remove specific subclasses from the Union since this was a specific
feature added in Python 3.7.

Bug: None
Test: act.py [...] -tc Sl4fSanityTest
Change-Id: Ia2778ce8d3ee60647652b41eca4341231e98d56d
diff --git a/acts/framework/acts/controllers/fuchsia_lib/ssh.py b/acts/framework/acts/controllers/fuchsia_lib/ssh.py
index a6fffad..59ebfc9 100644
--- a/acts/framework/acts/controllers/fuchsia_lib/ssh.py
+++ b/acts/framework/acts/controllers/fuchsia_lib/ssh.py
@@ -36,7 +36,7 @@
     """Result of an SSH command."""
 
     def __init__(
-        self, process: Union[subprocess.CompletedProcess[bytes],
+        self, process: Union[subprocess.CompletedProcess,
                              subprocess.CalledProcessError]
     ) -> None:
         self._raw_stdout = process.stdout