More docs cleanup (#7552)

* More docs improvements.

* timezone: mention which versions of AIX are supported.

plugins/callback/say.py

@@ -18,8 +18,6 @@ DOCUMENTATION = '''
     short_description: notify using software speech synthesizer
     description:
       - This plugin will use the C(say) or C(espeak) program to "speak" about play events.
-    notes:
-      - In Ansible 2.8, this callback has been renamed from C(osx_say) into M(community.general.say).
 '''
 
 import platform

plugins/callback/slack.py

@@ -18,7 +18,6 @@ DOCUMENTATION = '''
     short_description: Sends play events to a Slack channel
     description:
         - This is an ansible callback plugin that sends status updates to a Slack channel during playbook execution.
-        - Before Ansible 2.4 only environment variables were available for configuring this plugin.
     options:
       webhook_url:
         required: true

plugins/callback/syslog_json.py

@@ -16,7 +16,6 @@ DOCUMENTATION = '''
     short_description: sends JSON events to syslog
     description:
       - This plugin logs ansible-playbook and ansible runs to a syslog server in JSON format.
-      - Before Ansible 2.9 only environment variables were available for configuration.
     options:
       server:
         description: Syslog server that will receive the event.