fix taint-transparent syntax to lose lexical context

When submodules were introduced, the handling of taint-transparent
syntax changed to keep its lexical context. Restore the original
behavior, which is necessary to protect bindings, and fix taint
handling on submodules.
fix mzlib tests for use-before-initialization
plt-web/build: don't run as test
meta/new-web: omit "sync.rkt" when testing
scribble test: update expected result for `struct` indentation
racket/unit: fix test for use-before-definition
fix props for removed file