benchmark: remove broken string-creation.js

Strings where never mutable, it is not clear what this benchmarks
attempts to do. This did work at some point, but only because the
benchmark wasn't using strict mode.

PR-URL: https://github.com/nodejs/node/pull/7094
Reviewed-By: Trevor Norris <trev.norris@gmail.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Anna Henningsen <anna@addaleax.net>

benchmark/misc/string-creation.js

@@ -1,17 +0,0 @@
-'use strict';
-
-var common = require('../common.js');
-var bench = common.createBenchmark(main, {
-  millions: [100]
-});
-
-function main(conf) {
-  var n = +conf.millions * 1e6;
-  bench.start();
-  var s;
-  for (var i = 0; i < n; i++) {
-    s = '01234567890';
-    s[1] = 'a';
-  }
-  bench.end(n / 1e6);
-}