remove pure virtual from rsocketstats

[ragansa]

Shall we also remove NoopStats? Since it not doesn't do anything unique now. Although, it's name is nice and clear about it's purpose.. Thoughts?

[dymk]

Why though? Default methods are easy enough to add in base classes.

[ragansa]

Every time we update, someone has to go through and add the new, unused functions to every class that's inheriting.