perf lock: Remove unused struct lock_contention_key

The struct lock_contention_key is never used, remove it.
Signed-off-by: Yuan Can <yuancan@huawei.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/linux-perf-users/20220927013931.110475-6-yuancan@huawei.comSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/util/bpf_lock_contention.c

@@ -15,11 +15,6 @@
 
 static struct lock_contention_bpf *skel;
 
-/* should be same as bpf_skel/lock_contention.bpf.c */
-struct lock_contention_key {
-	s32 stack_id;
-};
-
 struct lock_contention_data {
 	u64 total_time;
 	u64 min_time;