Remove documentation references to "pg_dumps/development-image.sql".

There is no such file. Seeding is accomplised via the rake tasks as of
9ab743f351.

script/osx_dev

@@ -87,10 +87,6 @@ fi
 
 brew services start redis
 
-## Load seed data ##
-echo "Loading seed data..."
-psql -d discourse_development < pg_dumps/development-image.sql
-
 ## Install gems ##
 echo "Installing gems..."
 bundle install
@@ -103,4 +99,4 @@ rake db:seed_fu
 
 ## Run tests ##
 echo "Done! Running tests..."
-bundle exec rspec
+bundle exec rspec