servo: Merge #7240 - Stop using [T]::tail (from Ms2ger:slice_extras); r=nox

It has been removed upstream (rust-lang/rust#27684).

Source-Repo: https://github.com/servo/servo
Source-Revision: 4d7dd66ec9f0a5229a52b3301ac1a38848ebfb4b

UltraBlame original commit: 4fb4c524dac38483cbe495c72ff641d99b03c0d6

Author: marco-c

servo/tests/reftest.rs

@@ -11,7 +11,6 @@
 #![feature(exit_status)]
 #![feature(fs_walk)]
 #![feature(path_ext)]
-#![feature(slice_extras)]
 #![feature(slice_patterns)]
 #![feature(test)]
 
@@ -44,7 +43,7 @@ bitflags!(
 
 fn main() {
     let args: Vec<String> = env::args().collect();
-    let mut parts = args.tail().split(|e| &**e == "--");
+    let mut parts = args[1..].split(|e| &**e == "--");
 
     let harness_args = parts.next().unwrap();  
     let servo_args = parts.next().unwrap_or(&[]);