test/fiber/test_scheduler.rb: Remove the test file from $LOADED_FEATURES

to prevent the following failure on `make test-all --repeat-count=2`

http://ci.rvm.jp/results/trunk-repeat20-asserts@phosphorus-docker/3957774
```
  1) Error:
TestFiberScheduler#test_autoload:
NameError: uninitialized constant TestFiberSchedulerAutoload
          Object.const_get(:TestFiberSchedulerAutoload)
                ^^^^^^^^^^
```

1 files changed, 1 insertions, 0 deletions

diff --git a/test/fiber/test_scheduler.rb b/test/fiber/test_scheduler.rb
index 08ac386c29..f1030ea3fa 100644
--- a/test/fiber/test_scheduler.rb
+++ b/test/fiber/test_scheduler.rb
@@ -121,6 +121,7 @@ class TestFiberScheduler < Test::Unit::TestCase
 
     thread.join
   ensure
+    $LOADED_FEATURES.delete(File.expand_path("autoload.rb", __dir__))
     Object.send(:remove_const, :TestFiberSchedulerAutoload)
   end
 end