Nashorn Parser eagerly transform deletes

Nashorn's parser eagerly transforms delete expressions whose arguments are neither ident nodes nor base nodes. This leads to Parser API producing unexpected results, e.g. for:

function x() { }; delete x();

These kinds of transformations should be left to Lower. Also, it was kinda hacky how it was inserting expression statements for side effects. COMMARIGHT expression is much nicer for that purpose.