remove several mentions of list of bytes in predicate descriptions

remove several mentions of list of bytes in predicate descriptions

This is to focus more on the intended core representation of text: In
Prolog, text is ideally represented as a list of characters, and this
is what we want to encourage, especially given Scryer's compact
representation for strings.

For the time being, library(crypto) still also supports lists of bytes in
several predicates. This will likely be removed at some point in the
future. Please use lists of characters to make your code future-proof.