Tests: fix: leak of trigger in trigger listing tests

Tests: fix: leak of trigger in trigger listing tests

==1480456==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 112 byte(s) in 1 object(s) allocated from:
    #0 0x7fdb9260cfb9 in __interceptor_calloc /usr/src/debug/gcc/libsanitizer/asan/asan_malloc_linux.cpp:154
    #1 0x7fdb9242348d in zmalloc_internal ../../src/common/macros.hpp:60
    #2 0x7fdb924295a9 in lttng_trigger* zmalloc<lttng_trigger>() ../../src/common/macros.hpp:89
    #3 0x7fdb92423dbe in lttng_trigger_create /home/jgalar/EfficiOS/src/lttng-tools/src/common/trigger.cpp:58
    #4 0x56304832331f in register_trigger /home/jgalar/EfficiOS/src/lttng-tools/tests/regression/tools/trigger/utils/register-some-triggers.cpp:24
    #5 0x5630483233f1 in register_trigger_action_list_notify /home/jgalar/EfficiOS/src/lttng-tools/tests/regression/tools/trigger/utils/register-some-triggers.cpp:46
    #6 0x5630483239a0 in test_session_rotation_conditions /home/jgalar/EfficiOS/src/lttng-tools/tests/regression/tools/trigger/utils/register-some-triggers.cpp:246
    #7 0x563048323d4d in main /home/jgalar/EfficiOS/src/lttng-tools/tests/regression/tools/trigger/utils/register-some-triggers.cpp:309
    #8 0x7fdb91c6630f in __libc_start_call_main (/usr/lib/libc.so.6+0x2d30f)

Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>
Change-Id: Ie163989a70f65f9c2c4e93c36cc9fc6ba6bdeeb5