librustc: remove unnecessary `as_mut_slice` calls

src/librustc/metadata/cstore.rs

@@ -172,7 +172,7 @@ fn visit(cstore: &CStore, cnum: ast::CrateNum,
         for (&num, _) in self.metas.borrow().iter() {
             visit(self, num, &mut ordering);
         }
-        ordering.as_mut_slice().reverse();
+        ordering.reverse();
         let mut libs = self.used_crate_sources.borrow()
             .iter()
             .map(|src| (src.cnum, match prefer {

src/librustc/session/config.rs

@@ -764,7 +764,7 @@ pub fn build_session_options(matches: &getopts::Matches) -> Options {
             }
         }
     };
-    output_types.as_mut_slice().sort();
+    output_types.sort();
     output_types.dedup();
     if output_types.len() == 0 {
         output_types.push(OutputTypeExe);