drm/msm/dpu: remove QoS teardown on plane destruction

There is little point in disabling QoS on plane destruction: it happens
during DPU device destruction process, after which there will be no
running planes.

Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Patchwork: https://patchwork.freedesktop.org/patch/570049/
Link: https://lore.kernel.org/r/20231201211845.1026967-9-dmitry.baryshkov@linaro.org