feat(config): remove default preprocessors (coffee, html2js)

This should have been done in e033d56.

We don't ship any plugin with Karma anymore.
Users should rather use `karma init`, which installs plugins for them.

lib/config.js

@@ -203,7 +203,7 @@ var Config = function() {
  this.captureTimeout = 60000;
  this.proxies = {};
  this.proxyValidateSSL = true;
- this.preprocessors = {'**/*.coffee': 'coffee', '**/*.html': 'html2js'};
+ this.preprocessors = {};
  this.urlRoot = '/';
  this.reportSlowerThan = 0;
  this.loggers = [constant.CONSOLE_APPENDER];