refactor Remove dead code

Remove variables that are created but never used (in some cases, remove the variable entirely; in some case, just call the method without storing the result).

Add JSHint build-time check (for `src` files only) for declared but unused vars.

Also, fixes a minor issue that landed in
https://github.com/ariatemplates/ariatemplates/commit/107507a30d0407e46bcbf6dea3cf31ee28c43928#commitcomment-4166998

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Code review note:
In some cases, instead of removing the lines, I've commented them out -- usually in case of storing locally `args.something.something`, perhaps this will be useful in the future to know of existence of some param. But I can remove that also.