Rename User#delete to User#destroy

"delete" is generally used for immediate SQL deletion without running
any callbacks or other ruby code, whereas "destroy" will trigger callbacks.

Although we don't currently use any callbacks, let's rename this method to
align better with the convention.

app/models/user.rb

@@ -241,8 +241,8 @@ class User < ApplicationRecord
   end
 
   ##
-  # delete a user - leave the account but purge most personal data
-  def delete
+  # destroy a user - leave the account but purge most personal data
+  def destroy
     avatar.purge_later
 
     self.display_name = "user_#{id}"