Document the deprecated functions EVP_set_pw_prompt(3) and

Document the deprecated functions EVP_set_pw_prompt(3) and
EVP_get_pw_prompt(3) because some software out there still uses them.

While here, also improve the description of EVP_read_pw_string(3).

Delete documentation for des_read_pw(3) and des_read_pw_string(3).
They couldn't be used in LibreSSL since at least 2016 because they
were never in Symbols.list, and in 2022, jsing@ also removed them
from <openssl/ui_compat.h>.

Delete the misleading AUTHORS section.  Richard Levitte did not
write the original implementation of these functions, and the
compatibility wrapper around the UI_process(3) API that he did
write is not notable enough to be mentioned so prominently.