Remove normalize trial variables method

This is a bad idea for this plugin, since check_fn is a function. Need to figure out a way to protect variables like this one. For now, just revert to no functions as trial variables for this plugin.

plugins/jspsych-html.js

@@ -56,7 +56,7 @@ Example Usage:
             // if any trial variables are functions
             // this evaluates the function and replaces
             // it with the output of the function
-            trial = jsPsych.normalizeTrialVariables(trial);
+            // trial = jsPsych.normalizeTrialVariables(trial);
 
             var url = trial.url;
             if (trial.force_refresh) {