Ensure that specbind arg is always bare symbol, and drop check

Ensure that specbind arg is always bare symbol, and drop check

* src/eval.c (FletX, Flet, internal_lisp_condition_case)
(funcall_lambda): Ensure that the first argument to `specbind` is
a bare symbol in the few cases where this isn't statically guaranteed.
(specbind): Drop the symbol argument type check on the fast path.

(cherry picked from commit 0a57dfcff8d0abcf4427cfbfd886264bb3b8eaab)