Manually revert "Ensure allocation size fits into size_t"

This reverts commit cc9c5689

 for the file
pbe_scrypt.c instead of scrypt.c

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Richard Levitte <levitte@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4357)