Merge pull request rust-lang#1838 from folkertdev/c-variadic-remove-safe-keyword

remove the `safe` keyword from a c-variadic foreign function.

Author: ehuss

src/items/external-blocks.md

@@ -176,7 +176,7 @@ identifier.
 
 ```rust
 unsafe extern "C" {
-    safe fn foo(...);
+    unsafe fn foo(...);
     unsafe fn bar(x: i32, ...);
     unsafe fn with_name(format: *const u8, args: ...);
 }