Remove unnecessary tests before delete.
Remove obsolete GPU-related code.
Replace calls to the accessor function GetStep() with the member variable 'step'.

While the compiler will most likely take care of this (i.e. this is not an efficiency issue), the various calls to GetStep() made it inconvenient to step through while debugging.
Fixes to `Vequal()` and `Qequal()`

- Fix bug in `Vequal()` which was comparing addresses instead of vectors.
- Change `Qequal()` to return a bool and implement it in terms of the quaternion equality operator.
- Change arguments to const references.
Cleanup of static functions for operations on vectors and quaternions.

Use const references for arguments to prevent unnecessary copies.
Cleanup the `Qnotnull()` function.

- Change return value to bool
- Use const reference for argument

**Note**: it is questionable how appropriate this function is to begin with, as it involves floating point comparisons...
Use cont reference for argument of `SetRot()`
Use const references for arguments of `ChLinkMarkers::Initialize()`
Use const member functions in ChObject
Eliminate `ChLinkMarkers::SetMarkers()`

Simply replace it with calls to SetMarker1() and SetMarker2()