string/test_ellipsize.rb: remove non-sense tests

* test/-ext-/string/test_ellipsize.rb (Test_StringEllipsize#test_nonascii):
  rb_str_ellipsize() does not support BOM.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@43032 b2dd03c8-39d4-4d8f-98ff-823fe69b080e