perf lock: Remove unused struct lock_contention_key

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.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>