relayd: make functions static in ctf-trace.c

relayd: make functions static in ctf-trace.c

Fixes:

      CC       ctf-trace.o
    /home/smarchi/src/lttng-tools/src/bin/lttng-relayd/ctf-trace.c:47:6: error: no previous declaration for ‘ctf_trace_destroy’ [-Werror=missing-declarations]
     void ctf_trace_destroy(struct ctf_trace *trace)
          ^~~~~~~~~~~~~~~~~
    /home/smarchi/src/lttng-tools/src/bin/lttng-relayd/ctf-trace.c:62:6: error: no previous declaration for ‘ctf_trace_release’ [-Werror=missing-declarations]
     void ctf_trace_release(struct urcu_ref *ref)
          ^~~~~~~~~~~~~~~~~

Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Change-Id: I4c7ff97b3350d2e50530fb0666c5a7d02599f99f
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>