chore: Remove delete Instagram story implementation (#11097)

Currently, Instagram stories are downloaded and displayed as
attachments. We previously implemented story deletion by checking
individual messages via
https://github.com/chatwoot/chatwoot/pull/5300/files#diff-684a16c1b0b4c099fcdfeed95b1820e11fef629fe332ec7ce6a8c600331dd06dR110,
but this approach proved impractical and was removed. This PR removes
all unused code to avoid confusion. We will revisit the story deletion
feature when we implement `instagram_manage_insights`.

app/models/message.rb

@@ -155,15 +155,6 @@ class Message < ApplicationRecord
     }
   end
 
-  # TODO: We will be removing this code after instagram_manage_insights is implemented
-  # Better logic is to listen to webhook and remove stories proactively rather than trying
-  # a fetch every time a message is returned
-  def validate_instagram_story
-    inbox.channel.fetch_instagram_story_link(self)
-    # we want to reload the message in case the story has expired and data got removed
-    reload
-  end
-
   def merge_sender_attributes(data)
     data[:sender] = sender.push_event_data if sender && !sender.is_a?(AgentBot)
     data[:sender] = sender.push_event_data(inbox) if sender.is_a?(AgentBot)