test: refactor test-tick-processor

The test does some extra work that isn't necessary because of the way
temp directories are handled. The test removes all files from the temp
directory with `common.refreshTmpDir()` but still filters the results
even though only its files will be in the directory).

Refactor to remove that unneeded logic.

PR-URL: https://github.com/nodejs/node/pull/8180
Reviewed-By: Evan Lucas <evanlucas@me.com>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

test/parallel/test-tick-processor.js

@@ -45,12 +45,10 @@ runTest(/RunInDebugContext/,
 
 function runTest(pattern, code) {
   cp.execFileSync(process.execPath, ['-prof', '-pe', code]);
-  var matches = fs.readdirSync(common.tmpDir).filter(function(file) {
-    return /^isolate-/.test(file);
-  });
-  if (matches.length != 1) {
-    common.fail('There should be a single log file.');
-  }
+  var matches = fs.readdirSync(common.tmpDir);
+
+  assert.strictEqual(matches.length, 1, 'There should be a single log file.');
+
   var log = matches[0];
   var out = cp.execSync(process.execPath +
                         ' --prof-process --call-graph-size=10 ' + log,