* ext/socket/extconf.rb: don't test sys/feature_tests.h which is not
  used now.
  It was included in r7901 as "bug of gcc 3.0 on Solaris 8 ?".



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39265 b2dd03c8-39d4-4d8f-98ff-823fe69b080e