Remove test case that assumes FromStr provides TryFrom<&'a str>.

See https://travis-ci.org/rust-lang/rust/jobs/269861252

Author: jimmycuadra

src/libcore/tests/char.rs

@@ -32,7 +32,6 @@ fn test_convert() {
 #[test]
 fn test_from_str() {
     assert_eq!(char::from_str("a").unwrap(), 'a');
-    assert_eq!(char::try_from("a").unwrap(), 'a');
     assert_eq!(char::from_str("\0").unwrap(), '\0');
     assert_eq!(char::from_str("\u{D7FF}").unwrap(), '\u{d7FF}');
     assert!(char::from_str("").is_err());