Revert "[action] [PR:18699] fix: correct DUT variable name in startup tsa pretest (#344)" (#359)

This reverts commit 7551587.

I thought we cherry picked the multithreading run of pretest PR
(sonic-net/sonic-mgmt#17493) into msft.202405
but we never did, so the PR
sonic-net/sonic-mgmt#18699 should never be
cherry picked into msft.202405 as it's only a fix when test_pretest.py
runs with multithreading.

In msft.202405 branch, we are running test_pretest.py (e.g.
test_disable_startup_tsa_tsb_service()) in a normal for loop:
https://github.com/Azure/sonic-mgmt.msft/blob/202405/tests/test_pretest.py#L385,
so we should use duthost instead of dut

Author: yejianquan

tests/test_pretest.py

@@ -394,7 +394,7 @@ def test_disable_startup_tsa_tsb_service(duthosts, localhost):
                 duthost.shell("sudo mv {} {}".format(startup_tsa_tsb_file_path, backup_tsa_tsb_file_path))
                 output = duthost.shell("TSB", module_ignore_errors=True)
                 pytest_assert(not output['rc'], "Failed TSB")
-                dut.shell("sudo config save -y")
+                duthost.shell("sudo config save -y")
         else:
             logger.info("{} file does not exist in the specified path on dut {}".
                         format(startup_tsa_tsb_file_path, duthost.hostname))