Omit 'type=text/javascript' attribute in html script tag

[sal-bock]

Motivation:

Authors are encouraged to omit the attribute if the script refers to JavaScript code rather than specify a MIME type. The w3c validator will report warnings if we do so :-(

We should only provide the type attribute when necessary. e.g in ERXJavaScript a binding type="module", when the referenced file is a javascript module

[sal-bock]

Not setting the property er.extensions.ERXResponseRewriter.javascriptTypeAttribute=true did make a lot of type attributes go away. But this property does not influence the ERXJavaScript component.