Remove the disabled PVD integration

The PHYSX_ENABLE_PVD switch has never done anything. PX_SUPPORT_PVD is
not defined when we build PhysX, which compiles every PVD call site in
it out, so the PxPvd instance the switch creates and hands to
PxCreatePhysics() is ignored. Setting the switch to 1 would therefore
have connected to the PVD application and shown nothing.

Drop the switch and the objects it managed. Reviving PVD would mean
building PhysX with PX_SUPPORT_PVD=1 as well, which is a bigger decision
than flipping a define here, and this commit is where to find the code
that did the Qt side of it.

Pick-to: 6.12 6.11 6.8
Change-Id: I136fd044b2eaea0d8cf13cb1ee82e2c4c5cf88bc
Reviewed-by: Kristoffer Skau <kristoffer.skau@qt.io>