chore(rails): remove 5.0 leftovers (#2760)

Author: solnic

sentry-rails/spec/dummy/test_rails_app/app.rb

@@ -25,8 +25,6 @@ class TestApp < Rails::Application
 
 FILE_NAME =
   case Gem::Version.new(Rails.version)
-  when ->(v) { v < v5_2 }
-    "5-0"
   when ->(v) { v.between?(v5_2, v6_0) }
     "5-2"
   when ->(v) { v.between?(v6_0, v6_1) }