Revert "drm/lima: add usage counting method to ctx_mgr"

This reverts commit bccafec9.

This is due to the depend commit has been reverted on upstream:
commit baad1097 ("Revert "drm/scheduler: track GPU active time per entity"")

Acked-by: Emil Velikov <emil.l.velikov@gmail.com>
Signed-off-by: Qiang Yu <yuq825@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230404002601.24136-4-yq882255@163.com