disable PAPI in default thornlist

PAPI provides s set of performance counters that can be used with Cactus' timing infrastructure. However it only supports Linux as an operating system and compiling it on macOS (where it does then provide no counters) has been increasingly difficult.

Thus, similar to PETSc, it is proposed to disable PAPI in the default thornlist and enable it on clusters where it is know to work via simfactory’s enable-thhorns option.