Remove deprecated finder method calls

app/models/group.rb

@@ -193,7 +193,7 @@ class Group < ActiveRecord::Base
     deletions = Set.new(deletions.map{|d| map[d]})
 
     @deletions = []
-    group_users.delete_if do |gu|
+    group_users.each do |gu|
       @deletions << gu if deletions.include?(gu.user_id)
     end
 
@@ -221,7 +221,7 @@ class Group < ActiveRecord::Base
     if @deletions
       @deletions.each do |gu|
         gu.destroy
-        User.update_all 'primary_group_id = NULL', ['id = ? AND primary_group_id = ?', gu.user_id, gu.group_id]
+        User.where('id = ? AND primary_group_id = ?', gu.user_id, gu.group_id).update_all 'primary_group_id = NULL'
       end
     end
     @deletions = nil

app/models/topic.rb

@@ -200,7 +200,7 @@ class Topic < ActiveRecord::Base
         modifications: changes.extract!(:category_id, :title)
       )
 
-      Post.update_all({version: number}, id: first_post_id)
+      Post.where(id: first_post_id).update_all(version: number)
     end
   end