ggml : remove obsolete n_past assert in ggml_alibi

ggml.c

@@ -13064,8 +13064,6 @@ static void ggml_compute_forward_alibi_f32(
     float max_bias;
     memcpy(&max_bias, (int32_t *) dst->op_params + 2, sizeof(float));
 
-    assert(n_past >= 0);
-
     const int64_t ne0 = src0->ne[0]; // all_seq_len = n_past + ne1
     const int64_t ne1 = src0->ne[1]; // seq_len_without_past
     const int64_t ne2 = src0->ne[2]; // n_head -> this is k