test: remove redeclared var in test-domain

PR-URL: https://github.com/nodejs/node/pull/4984
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Johan Bergström <bugs@bergstroem.nu>
Reviewed-By: Michaël Zasso <mic.besace@gmail.com>

test/parallel/test-domain.js

@@ -175,7 +175,7 @@ function fn2(data) {
   assert.equal(data, 'data', 'should not be null err argument');
 }
 
-var bound = d.intercept(fn2);
+bound = d.intercept(fn2);
 bound(null, 'data');
 
 // intercepted should never pass first argument to callback