update copyright holders

src/Makefile.am

@@ -1,7 +1,6 @@
 # StarPU --- Runtime system for heterogeneous multicore architectures.
 #
 # Copyright (C) 2009-2020  Université de Bordeaux, CNRS (LaBRI UMR 5800), Inria
-# Copyright (C) 2012       Benjamin Lorendeau
 # Copyright (C) 2013       Simon Archipoff
 #
 # StarPU is free software; you can redistribute it and/or modify