[Flexiglass] Don't add MediaContainerView to the NSSL

NSSL had a 0 height, but visible MediaContainerView, which produced
a spacing gap after it, which offsetted the whole stack wrongly.

The new compose version of MediaContainerView doesn't use the NSSL
to place it, so it is safe to remove it now.

Fixes: 443055172
Fixes: 443052463
Test: check the paddings when media in compose is enabled
Flag: com.android.systemui.scene_container

Change-Id: Ib6f079aa39cbdf41828f1560b9642ecb70012bc5