argument FREE. Now the prompt string is always consumed. Updated
all callers.
* src/unix_interact.c (unix_read_password): Deleted fourth
argument FREE.

Rev: src/client_keyexchange.c:1.64
Rev: src/client_userauth.c:1.55
Rev: src/interact.h:1.12
Rev: src/lsh-writekey.c:1.34
Rev: src/spki.c:1.55
Rev: src/srp-gen.c:1.19
Rev: src/unix_interact.c:1.24