drm/i915: Remove unused live_context_for_engine

The last use of live_context_for_engine() was removed in 2021 by
commit 99919be7 ("drm/i915/gem: Zap the i915_gem_object_blt code")

Remove it.

Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250125003846.228514-1-linux@treblig.org


Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>