FIX: Don't display destroy reviewable button on client (#21226)

# Context

https://meta.discourse.org/t/missing-translate-in-review-page/262604

![image](https://user-images.githubusercontent.com/50783505/234089049-72332040-e7d5-4081-824a-b0b36e37187a.png)

An additional button was added as a result of dd495a0e19 which was intended to grant access to deleting reviewable from the API. 

We were being too flexible by only checking if the user was an admin

012aaf0ba3/lib/guardian.rb (L237)

where it should instead by scoped to check if the request was an API call.

# Fix

https://github.com/discourse/discourse/pull/21226/files#diff-0a2548be4b18bd4ef2dffb3ef8e44984d2fef7f037b53e98f67abea52ef75aa2R237

# Additions

Added a new guard of `is_api?`

https://github.com/discourse/discourse/pull/21226/files#diff-0a2548be4b18bd4ef2dffb3ef8e44984d2fef7f037b53e98f67abea52ef75aa2R657-R660

In `app/models/reviewable.rb` we check if the user has the permissions to the destroy action via the `Guardian`. To do this we were instantiating a new `Guardian` class which then caused us to lose the context of the request. The request is a necessary component in the guard of `is_api?` so we needed to pass the already defined Guardian from the `app/controllers/reviewables_controller.rb` to the `#perform` method to ensure the request is present.

app/controllers/reviewables_controller.rb

@@ -169,7 +169,7 @@ class ReviewablesController < ApplicationController
     reviewable = Reviewable.find_by(id: params[:reviewable_id], created_by: user)
     raise Discourse::NotFound.new if reviewable.blank?
 
-    reviewable.perform(current_user, :delete)
+    reviewable.perform(current_user, :delete, { guardian: @guardian })
 
     render json: success_json
   end