Remove obsolete test

This test was added long time ago and marked as ignored.
The same test was added later in #8485 as run-fail/issue-3907.rs,
but the old one was not deleted.
auto merge of #15033 : Sawyer47/rust/old-test, r=alexcrichton

This test was added long time ago and marked as ignored.
The same test was added later in #8485 as run-fail/issue-3907.rs,
but the old one was not deleted.