res_pjsip_pubsub: fixed a bug when pjsip_tx_data_dec_ref is called twice.

This patch removed call of pjsip_tx_data_dec_ref in send_notify
if send_request failed.
The pjsip_dlg_send_request deletes the message on error by itself.

It seems this patch fixes next issues:
ASTERISK-26199
ASTERISK-26166
ASTERISK-26174

Change-Id: I8b05917c93d993f95d604c042ace5f1a5500f59a