(maint) remove dead code in scope_spec

Commented out code was testing removed behavior. Removed comments.
(PUP-1166) Add better error message when turning on strict_variables

When turning on --strict_variables without also using --future parser
with the future evaluator, the raised error is an uncaught throw.
Now the error message is "Undefined Variable".
Merge pull request #2272 from hlindberg/pup-1166_better-error-for-strict-var-lookup

(PUP-1166) Add better error for 3x --strict_variables