perf/core: Remove unused local variable

Drop LIST_HEAD() where the variable it declares is never used.

Compiler probably never warned us, because the LIST_HEAD()
initializer is technically 'usage'.

[ mingo: Tweak changelog. ]

Signed-off-by: Haowen Bai <baihaowen@meizu.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/1653645835-29206-1-git-send-email-baihaowen@meizu.com