revert: "fix: message_type inconsistency across message end points" (#10119)

Reverts chatwoot/chatwoot#10108

spec/controllers/public/api/v1/inbox/messages_controller_spec.rb

@@ -26,7 +26,6 @@ RSpec.describe 'Public Inbox Contact Conversation Messages API', type: :request
       expect(response).to have_http_status(:success)
       data = response.parsed_body
       expect(data['content']).to eq('hello')
-      expect(data['message_type']).to eq(0)
     end
 
     it 'does not create the message' do