CLEANUP: sample: remove duplicate "stopping" sample fetch keyword

The "stopping" sample fetch keyword was accidently duplicated in 1.9
by commit 70fe94419 ("MINOR: sample: add cpu_calls, cpu_ns_avg,
cpu_ns_tot, lat_ns_avg, lat_ns_tot"). This has no effect so no
backport is needed.
diff --git a/src/sample.c b/src/sample.c
index ea60b93..81c96bb 100644
--- a/src/sample.c
+++ b/src/sample.c
@@ -4038,7 +4038,6 @@
 	{ "thread",       smp_fetch_thread,  0,          NULL, SMP_T_SINT, SMP_USE_INTRN },
 	{ "rand",         smp_fetch_rand,  ARG1(0,SINT), NULL, SMP_T_SINT, SMP_USE_INTRN },
 	{ "stopping",     smp_fetch_stopping, 0,         NULL, SMP_T_BOOL, SMP_USE_INTRN },
-	{ "stopping",     smp_fetch_stopping, 0,         NULL, SMP_T_BOOL, SMP_USE_INTRN },
 	{ "uuid",         smp_fetch_uuid,  ARG1(0, SINT),      smp_check_uuid, SMP_T_STR, SMP_USE_INTRN },
 
 	{ "cpu_calls",    smp_fetch_cpu_calls,  0,       NULL, SMP_T_SINT, SMP_USE_INTRN },