perf_builder: do not automatically pull game files
This requires that Steam game files are installed (manually) on the system prior to running AbnPerfBuilder. Some games (Dota2) require that the game is started once after install and prior to benchmarking, to insure that the correct settings are used. The rsync previously done here would cause Dota2 to revert to the lowest settings every time, since the original game on CI master was run on a KBL system (my dev laptop).