Move relay-experimental package as internal repo for faster iteration

Summary:
This commit removes `relay-experimental` from `fbsource` in favor of keeping it www only for now, which has the following benefits:

- Prevents accidental use in RN
- Allows us to use Hooks without being blocked on a specific react version being synced to fbsource/oss
- Allows us to iterate much quicker without having to wait on sync diffs and being able to test directly on Comet

WWW diff: D13324800

Reviewed By: kassens

Differential Revision: D13330052

fbshipit-source-id: 74c6efab0934e505189ebcb43de66ad51e31b8a2

fb-examples/config/facebook/relay.php-example

@@ -29,7 +29,6 @@ final class FacebookRelay extends FBShipItConfig {
   const string RELAY_COMPILER = self::RELAY_OSS.'relay-compiler/';
   const string RELAY_RUNTIME = self::RELAY_OSS.'relay-runtime/';
   const string RELAY_TEST_UTILS = self::RELAY_OSS.'relay-test-utils/';
-  const string RELAY_EXPERIMENTAL = self::RELAY_OSS.'relay-experimental/';
 
   <<__Override>>
   protected static function defaultProjectFilterChangeset(
@@ -60,7 +59,6 @@ final class FacebookRelay extends FBShipItConfig {
       self::RELAY_COMPILER => 'packages/relay-compiler/',
       self::RELAY_RUNTIME => 'packages/relay-runtime/',
       self::RELAY_TEST_UTILS => 'packages/relay-test-utils/',
-      self::RELAY_EXPERIMENTAL => 'packages/relay-experimental/',
     };
   }