Missing unregistering of drmgr's tls slot in drcachesim's func_trace

The func_trace in drcachesim registers a thread-local storage (tls) slot during initialization (func_trace_init()) but does not unregister this slot during exit (func_trace_exit()). This is problematic in a setting with multiples detaches and re-attaches and no resetting of the taken tls slots, since there is a slot that is not properly freed ("leaked" slot) potentially leading to a false shortage of available tls slots.