Racket: duplicate version check removed

We used to check for a good racket version during its start-up, but
these days we already have an independent version check before that.
Racket: fix for evaluations inside typed/racket modules

When evaluating (re)definitions in a typed module, it's necessary that
the form evaluated is wrapped with #%top-interaction, so that typed
racket's redefinition of that macro enters into play and the system
records the type information of the new value.

Many thanks to Sam Tobin-Hochstadt for the tip, and for his encouraging
words.