Reduce unused variable in _client_receive. (#686)

Remove unused variable in _client_receive.
diff --git a/mobly/controllers/android_device_lib/jsonrpc_client_base.py b/mobly/controllers/android_device_lib/jsonrpc_client_base.py
index 0e8608b..6d8a9d5 100644
--- a/mobly/controllers/android_device_lib/jsonrpc_client_base.py
+++ b/mobly/controllers/android_device_lib/jsonrpc_client_base.py
@@ -297,7 +297,6 @@
         """
         try:
             response = self._client.readline()
-            response_log = str(response)
             if self.verbose_logging:
                 self.log.debug('Snippet received: %s', response)
             else:
@@ -306,7 +305,7 @@
                 else:
                     self.log.debug(
                         'Snippet received: %s... %d chars are truncated',
-                        response_log[:_MAX_RPC_RESP_LOGGING_LENGTH],
+                        response[:_MAX_RPC_RESP_LOGGING_LENGTH],
                         len(response) - _MAX_RPC_RESP_LOGGING_LENGTH)
             return response
         except socket.error as e:
diff --git a/tests/mobly/controllers/android_device_lib/jsonrpc_client_base_test.py b/tests/mobly/controllers/android_device_lib/jsonrpc_client_base_test.py
index 063ab4e..583c52c 100755
--- a/tests/mobly/controllers/android_device_lib/jsonrpc_client_base_test.py
+++ b/tests/mobly/controllers/android_device_lib/jsonrpc_client_base_test.py
@@ -302,7 +302,7 @@
         # DEBUG level log should truncated by given length.
         client.log.debug.assert_called_with(
             'Snippet received: %s... %d chars are truncated',
-            str(testing_rpc_response)
+            testing_rpc_response
             [:jsonrpc_client_base._MAX_RPC_RESP_LOGGING_LENGTH],
             resp_len - jsonrpc_client_base._MAX_RPC_RESP_LOGGING_LENGTH)