drm/i915/trace: Remove unused frequency trace

Commit 3e7abf81 ("drm/i915: Extract GT render power state management")
removes the "trace_intel_gpu_freq_change()" trace points but
their definition was left without users. Remove it.

Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221011135940.367048-1-andi.shyti@linux.intel.com