threadpool: do not clear barrier counters between graphs computes (fixes race with small graphs)

This fixes the race condition with very small graphs where the main thread happens to
start a new graph while the workers are just about to exit from barriers.

Author: max-krasnyansky

ggml/src/ggml.c

@@ -19362,8 +19362,6 @@ enum ggml_status ggml_graph_compute(struct ggml_cgraph * cgraph, struct ggml_cpl
         threadpool->cgraph           = cgraph;
         threadpool->cplan            = cplan;
         threadpool->n_threads_cur    = n_threads;
-        threadpool->n_barrier        = 0;
-        threadpool->n_barrier_passed = 0;
         threadpool->current_chunk    = 0;
         threadpool->ec               = GGML_STATUS_SUCCESS;
     }