callbacks are cancelled. Updated callers to not use gc_final, only
io_final.

Rev: src/lsh-decode-key.c:1.11
Rev: src/lsh-export-key.c:1.11
Rev: src/lsh.c:1.148
Rev: src/lsh_proxy.c:1.25
Rev: src/lshd.c:1.125
Rev: src/lshg.c:1.15
Rev: src/sexp-conv.c:1.10
Rev: src/srp-gen.c:1.12