chore: remove unused telegram bot model (#12417)

## Summary
- remove unused TelegramBot model and its association
- drop obsolete telegram_bots table

app/models/account.rb

@@ -89,7 +89,6 @@ class Account < ApplicationRecord
   has_many :portals, dependent: :destroy_async, class_name: '::Portal'
   has_many :sms_channels, dependent: :destroy_async, class_name: '::Channel::Sms'
   has_many :teams, dependent: :destroy_async
-  has_many :telegram_bots, dependent: :destroy_async
   has_many :telegram_channels, dependent: :destroy_async, class_name: '::Channel::Telegram'
   has_many :twilio_sms, dependent: :destroy_async, class_name: '::Channel::TwilioSms'
   has_many :twitter_profiles, dependent: :destroy_async, class_name: '::Channel::TwitterProfile'

app/models/telegram_bot.rb

@@ -1,17 +0,0 @@
-# == Schema Information
-#
-# Table name: telegram_bots
-#
-#  id         :integer          not null, primary key
-#  auth_key   :string
-#  name       :string
-#  created_at :datetime         not null
-#  updated_at :datetime         not null
-#  account_id :integer
-#
-
-class TelegramBot < ApplicationRecord
-  belongs_to :account
-  has_one :inbox, as: :channel, dependent: :destroy_async
-  validates :auth_key, uniqueness: { scope: :account_id }
-end