Move GM hooks to where they belong

* Removed GM:PlayerDealth from cl_init since it's never called there
* Moved GM:OnPlayerChat to cl_init since it's a clientside only hook
* Made GM:GravGunPickupAllowed shared
* Moved GM:CanPlayerUnfreeze to to sandbox/player.lua since it's
serverside only function
* Moved GM:PlayerAuthor to serverside
* Removed GM:CanPose, GM:CanRender, GM:CanConstruct and GM:CanConstrain
since they are never called at all
* Removed GM:GetVehicles because there is no reason for it to exist, it
is never called and it serves no purpose
* Made so that the vehicle camera doesn't collide with anything but
world, this is to prevent third person fucking up when you have attached
props to the seat