repl: remove workaround for function redefinition

The issue is fixed upstream in V8. Thus we do not need this workaround
in REPL.

Fixes: nodejs#548
PR-URL: nodejs#9618
Reviewed-By: Ali Ijaz Sheikh <ofrobots@google.com>
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>

lib/repl.js

@@ -254,12 +254,6 @@ function REPLServer(prompt,
       // an expression.
       cmd = `(${cmd})`;
       self.wrappedCmd = true;
-    } else {
-      // Mitigate https://github.com/nodejs/node/issues/548
-      cmd = cmd.replace(
-        /^\s*function(?:\s*(\*)\s*|\s+)([^(]+)/,
-        (_, genStar, name) => `var ${name} = function ${genStar || ''}${name}`
-      );
     }
     // Append a \n so that it will be either
     // terminated, or continued onto the next expression if it's an