DEV: Cleanup todos from codebase (#30394)

This PR involves cleaning up the codebase from my (@keegangeorge's) todos. 

In particular:
- Remove Form Template related todos (these are no longer in the roadmap)
- Remove old left-over AI summarization related code after moving to AI (https://github.com/discourse/discourse-ai/pull/658)
- Update one form template related spec

lib/validators/summarization_validator.rb

@@ -1,21 +0,0 @@
-# frozen_string_literal: true
-
-# TODO(@keegan): Remove after removing SiteSetting.summarization_strategy
-
-class SummarizationValidator
-  def initialize(opts = {})
-    @opts = opts
-  end
-
-  def valid_value?(val)
-    strategy = Summarization::Base.find_strategy(val)
-
-    return true unless strategy
-
-    strategy.correctly_configured?.tap { |is_valid| @strategy = strategy unless is_valid }
-  end
-
-  def error_message
-    @strategy.configuration_hint
-  end
-end