Renaming of "args" fields in Rascal grammar

In order to eliminate name clashes with the "args" field of the "Tree"
datatype, the following renaming has been done in the definition of
non-terminal Prod: two occurrences of "Sym* args" have been renamed to
"Sym* syms"
Regenerated Rascal AST
Uncommented the addition of fields "prod" and "args".
Commented out print statements
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