Remove unused imports in merge_yaml

Dumper and Loader are classes seem to be loaded but not used in the merge_yaml
file. This change removes them for reducing the number of lines.

Change-Id: I87ef305903ab02226fcaa725ece622647d17811c

ansible/action_plugins/merge_yaml.py

@@ -21,13 +21,6 @@ import tempfile
 
 from yaml import dump
 from yaml import safe_load
-try:
-    from yaml import CDumper as Dumper  # noqa: F401
-    from yaml import CLoader as Loader  # noqa: F401
-except ImportError:
-    from yaml import Dumper  # noqa: F401
-    from yaml import Loader  # noqa: F401
-
 
 from ansible import constants
 from ansible import errors as ansible_errors