Log: libstonithd: Drop crm_perror() in st_client.c

Neither of these should have used crm_perror() in the first place,
because errno is not guaranteed to be meaningful. crm_ipc_send() returns
a legacy Pacemaker return code but doesn't set errno explicitly.

The only thing we lose here is writing the message to stderr for CLI
tools. However, CLI tools have verbose options. It doesn't seem worth
passing pcmk__output_t down the call chain... which would be even more
of a pain since it would have to go in the stonith_t private data
somehow.

Other errors in this file already simply use crm_err().

Ref T172

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>