scenarios: remove ncells@ scenario and define number of cells explicitly

the specific cell scenarios files already contain cell-related
information so having a extra ncells scenario seems too much overhead.
furthermore, in more complex tests its helps to reduce the filename/path
lenght to avoid hitting the 255 character limit

Change-Id: If022d9e8d239805ee1280fb52660e68dda7484a0
diff --git a/sysmocom/scenarios/mod-enb-cells-2ca.conf b/sysmocom/scenarios/mod-enb-cells-2ca.conf
index c9468c6..916d0eb 100644
--- a/sysmocom/scenarios/mod-enb-cells-2ca.conf
+++ b/sysmocom/scenarios/mod-enb-cells-2ca.conf
@@ -2,6 +2,7 @@
 modifiers:
   enb:
   - id: 0x19B
+    num_cells: 2
     cell_list:
     - cell_id: 0x00
       pci: 0x01