ScriptModule: remove unused code
ScriptModule: simplify run method

We can lean on ScriptService#eval directly, rather than asking for the
ScriptLanguage, getting a ScriptEngine and then calling its eval method.
ScriptInfo: add missing final keyword
ScriptInfo: add input parsing logic

This is in preparation for the removal of ScriptInputs and
simplification of ScriptService to lean on the new ScriptModule.
ScriptModule: remove unnecessary method override

We do not need to explicitly populate service and context parameters;
the ServicePreprocessor already exists to do that for us.