(since the repl test suite tests the pretty big language's repl and since there was a test case
there that would have discovered a bug that we only found in the hours before the release but had
been lurking for a few days)
Removed "info.rkt", since all entries were unused; switched ".ss" to
".rkt" in both real code and tested code (except for the teachpack
tests); modernized some tests to use symbolic requires (which would also
make it easier to deal with).