drm/i915/pmu: Remove i915_pmu_event_event_idx()

perf event already has a default function that returns 0, no need to
override with the same thing.

Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250113183329.3138138-1-lucas.demarchi@intel.com


Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>