Use $this->params insteand $app->getTemplate(true)->params at the templates

As requested (https://github.com/joomla/joomla-cms/pull/3782#discussion-diff-13786134) see here @bakual

old PR: https://github.com/joomla/joomla-cms/pull/3791
This is funny code here. I don't even understand what it is supposed to do but we don't want to overwrite the template params for sure.