Remove duplicate entries in .gitignore

The .gitignore could still be better organized

.gitignore

@@ -98,22 +98,14 @@ node_modules
 
 spec/examples.txt
 .postcssrc.yml
-/public/packs
-/public/packs-test
 /node_modules
-yarn-debug.log*
 .yarn-integrity
 
 # Ignore master key for decrypting credentials and more.
 /config/master.key
 /config/credentials.yml.enc
 
-/public/packs
-/public/packs-test
-/node_modules
 /yarn-error.log
-yarn-debug.log*
-.yarn-integrity
 /app/assets/builds/*
 !/app/assets/builds/.keep
 !/app/assets/builds/.gitkeep