Remove redundant .all in .all.sample calls

Rubocop doesn't detect this method because we've added it in the
ApplicationRecord class, but we're removing the `.all` calls for
consistency.

db/dev_seeds/communities.rb

@@ -5,15 +5,15 @@ end
 
 section "Creating Communities Topics" do
   Community.find_each do |community|
-    Topic.create(community: community, author: User.all.sample,
+    Topic.create(community: community, author: User.sample,
                  title: Faker::Lorem.sentence(word_count: 3).truncate(60), description: Faker::Lorem.sentence)
   end
 end
 
 section "Commenting Community Topics" do
   30.times do
-    author = User.all.sample
-    topic = Topic.all.sample
+    author = User.sample
+    topic = Topic.sample
     Comment.create!(user: author,
                     created_at: rand(topic.created_at..Time.current),
                     commentable: topic,