Remove deprecated DISPLAY_SKIPPED_HOSTS env var (#77427)

Fixes #77396

changelogs/fragments/77396-remove-display_skipped_hosts.yml

@@ -0,0 +1,2 @@
+removed_features:
+  - Remove deprecated ``DISPLAY_SKIPPED_HOSTS`` environment variable (https://github.com/ansible/ansible/issues/77396)

lib/ansible/config/base.yml

@@ -1227,11 +1227,6 @@ DISPLAY_SKIPPED_HOSTS:
   default: True
   description: "Toggle to control displaying skipped task/host entries in a task in the default callback"
   env:
-  - name: DISPLAY_SKIPPED_HOSTS
-    deprecated:
-      why: environment variables without ``ANSIBLE_`` prefix are deprecated
-      version: "2.12"
-      alternatives: the ``ANSIBLE_DISPLAY_SKIPPED_HOSTS`` environment variable
   - name: ANSIBLE_DISPLAY_SKIPPED_HOSTS
   ini:
   - {key: display_skipped_hosts, section: defaults}

lib/ansible/plugins/doc_fragments/default_callback.py

@@ -16,11 +16,6 @@ class ModuleDocFragment(object):
         type: bool
         default: yes
         env:
-          - name: DISPLAY_SKIPPED_HOSTS
-            deprecated:
-              why: environment variables without C(ANSIBLE_) prefix are deprecated
-              version: "2.12"
-              alternatives: the C(ANSIBLE_DISPLAY_SKIPPED_HOSTS) environment variable
           - name: ANSIBLE_DISPLAY_SKIPPED_HOSTS
         ini:
           - key: display_skipped_hosts