Remove TRT stand-alone from InDet Track Particles, except when kept due to e/gamma

Mentioning @jcatmore , @hgray , @elmsheus .

I think this is something we have been discussing on various AOD reduction TF.

This is a take on removing TRT-alone also from the InDet container , except when an egamma object is associated with them.

If I recall correctly this is not a huge gain (I think is like 2%) but I think is something we wanted to do ...