TruffleRuby does not provide 'bin/testrb' anymore.

Author: ansalond

mx.truffleruby/mx_truffleruby.py

@@ -153,7 +153,6 @@ def ruby_testdownstream_sulong(args):
         'bin/rake',
         'bin/rdoc',
         'bin/ri',
-        'bin/testrb',
     ],
     launcher_configs=[
         mx_sdk.LanguageLauncherConfig(