drm/v3d: Don't increment `enabled_ns` twice

The commit 509433d8 ("drm/v3d: Expose the total GPU usage stats on sysfs")
introduced the calculation of global GPU stats. For the regards, it used
the already existing infrastructure provided by commit 09a93cc4 ("drm/v3d:
Implement show_fdinfo() callback for GPU usage stats"). While adding
global GPU stats calculation ability, the author forgot to delete the
existing one.

Currently, the value of `enabled_ns` is incremented twice by the end of
the job, when it should be added just once. Therefore, delete the
leftovers from commit 509433d8 ("drm/v3d: Expose the total GPU usage
stats on sysfs").

Fixes: 509433d8 ("drm/v3d: Expose the total GPU usage stats on sysfs")
Reported-by: Tvrtko Ursulin <tursulin@igalia.com>
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Reviewed-by: Jose Maria Casanova Crespo <jmcasanova@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240403203517.731876-2-mcanal@igalia.com