Fix 28 Byte Dimensions Object

- the `virtual ~Destructor` blows up the object from 3x8=24 to *28 bytes*
- no-one inherits from Dimensions, so a *virtual destructor* is **not necessary**
- &object (instead of .getPointer() ) calls will create corrupted data, for example all PIConGPU [Dimensions](https://github.com/ComputationalRadiationPhysics/picongpu/blob/master/src/picongpu/include/plugins/output/HDF5Writer.hpp#L526-L528) attributes ([here](https://github.com/ComputationalRadiationPhysics/picongpu/blob/master/src/picongpu/include/plugins/output/HDF5Writer.hpp#L574-L575), too) are corrupted, due to wrong usage of `&dimObj` instead `dimObj.getPointer()`