[vstest]: unmark fixture for create/remove_dpb_config_file (#1307)

Fixture "create_dpb_config_file" called directly. Fixtures are not meant to be called directly,
but are created automatically when test functions request them as parameters.
See https://docs.pytest.org/en/latest/fixture.html for more information about fixtures, and
https://docs.pytest.org/en/latest/deprecations.html#calling-fixtures-directly about how to update your code.

Signed-off-by: Guohan Lu <lguohan@gmail.com>

tests/conftest.py

@@ -1017,7 +1017,6 @@ def dvs_acl_manager(request, dvs):
                                          dvs.get_counters_db())
 
 ##################### DPB fixtures ###########################################
-@pytest.yield_fixture(scope="module")
 def create_dpb_config_file(dvs):
     cmd = "sonic-cfggen -j /etc/sonic/init_cfg.json -j /tmp/ports.json --print-data > /tmp/dpb_config_db.json"
     dvs.runcmd(['sh', '-c', cmd])
@@ -1026,7 +1025,6 @@ def create_dpb_config_file(dvs):
     cmd = "cp /tmp/dpb_config_db.json /etc/sonic/config_db.json"
     dvs.runcmd(cmd)
 
-@pytest.yield_fixture(scope="module")
 def remove_dpb_config_file(dvs):
     cmd = "mv /etc/sonic/config_db.json.bak /etc/sonic/config_db.json"
     dvs.runcmd(cmd)