removed obsolete compatibility layer in tests

 /*global casper*/
 /*jshint strict:false*/
-// skip this test for phantom versions < 1.5
-if (phantom.version.major === 1 && phantom.version.minor < 6) {
-    casper.test.comment('Skipped tests, PhantomJS 1.6 required');
-    casper.test.done();
-} else {
-    casper.setFilter('page.prompt', function(message, value) {
-        return 'Chuck ' + value;
-    });
+casper.setFilter('page.prompt', function(message, value) {
+    return 'Chuck ' + value;
+});
 
-    casper.start('tests/site/prompt.html', function() {
-        this.test.assertEquals(this.getGlobal('name'), 'Chuck Norris', 'prompted value has been received');
-    });
+casper.start('tests/site/prompt.html', function() {
+    this.test.assertEquals(this.getGlobal('name'), 'Chuck Norris', 'prompted value has been received');
+});
 
-    casper.run(function() {
-        this.test.done();
-    });
-}
+casper.run(function() {
+    this.test.done();
+});