[PR #10873/6cd46654 backport][stable-11] Avoid six in plugin code (#10875)

Avoid six in plugin code (#10873)

Avoid six in plugin code.

(cherry picked from commit 6cd4665412)

Co-authored-by: Felix Fontein <felix@fontein.de>

plugins/lookup/flattened.py

@@ -37,7 +37,6 @@ _raw:
   type: list
 """
 from ansible.errors import AnsibleError
-from ansible.module_utils.six import string_types
 from ansible.plugins.lookup import LookupBase
 from ansible.utils.listify import listify_lookup_plugin_terms
 
@@ -65,7 +64,7 @@ class LookupModule(LookupBase):
                 # ignore undefined items
                 break
 
-            if isinstance(term, string_types):
+            if isinstance(term, str):
                 # convert a variable to a list
                 term2 = listify_lookup_plugin_terms(term, templar=self._templar)
                 # but avoid converting a plain string to a list of one string