drm/msm/dpu: drop dpu_core_perf_destroy()

This function does nothing, just clears one struct field. Drop it now.

Acked-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Reviewed-by: Abhinav Kumar <quic_abhinavk@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/550210/
Link: https://lore.kernel.org/r/20230730010102.350713-11-dmitry.baryshkov@linaro.org