makefile should not die if there are no files to remove
makefile should not die if there are no files to remove

--HG--
extra : convert_revision : 543f0197ee7d37b43cc51b32ccf83572454fffab

davetcoleman/ompl,florianhauer/ompl,jvgomez/ompl,jvgomez/ompl,sonny-tarbouriech/ompl,jvgomez/ompl,florianhauer/ompl,sonny-tarbouriech/ompl,utiasASRL/batch-informed-trees,utiasASRL/batch-informed-trees,florianhauer/ompl,sonny-tarbouriech/ompl,sonny-tarbouriech/ompl,utiasASRL/batch-informed-trees,utiasASRL/batch-informed-trees,utiasASRL/batch-informed-trees,florianhauer/ompl,davetcoleman/ompl,jvgomez/ompl,davetcoleman/ompl,davetcoleman/ompl,davetcoleman/ompl,jvgomez/ompl,florianhauer/ompl,sonny-tarbouriech/ompl,utiasASRL/batch-informed-trees,florianhauer/ompl,davetcoleman/ompl,jvgomez/ompl,sonny-tarbouriech/ompl