rustc_back: Remove unneeded explicit variable

This value is the default anyway

Author: alexcrichton

src/librustc_back/target/linux_base.rs

@@ -13,7 +13,6 @@ use std::default::Default;
 
 pub fn opts() -> TargetOptions {
     TargetOptions {
-        linker: "cc".to_string(),
         dynamic_linking: true,
         executables: true,
         morestack: true,