improved gap junction documentation

extras/userdoc/md/documentation/simulations-with-gap-junctions.md

@@ -13,18 +13,7 @@ The synapse model to create a gap-junction connection is named `gap_junction`.
 Unlike chemical synapses gap junctions are bidirectional connections. 
 In order to create **one** accurate gap-junction connection 
 **two** NEST connections are required:
-
-```python
-import nest
-
-a = nest.Create('hh_psc_alpha_gap')
-b = nest.Create('hh_psc_alpha_gap')
-# Create gap junction between neurons a and b
-nest.Connect(a, b, {'rule': 'one_to_one'}, {'model': 'gap_junction', 'weight': 0.5})
-nest.Connect(b, a, {'rule': 'one_to_one'}, {'model': 'gap_junction', 'weight': 0.5})
-```
-
-Thus for each created connection a second connection with the exact same parameters 
+For each created connection a second connection with the exact same parameters 
 in the opposite direction is required.
 NEST provides the possibility to create both connections with a single call to `nest.Connect`
 via the `make_symmetric` flag (default value: `False`) of the connection dictionary:
@@ -45,9 +34,6 @@ is restricted to
 - `one_to_one` connections with `'make_symmetric': True`
 - `all_to_all` connections with equal source and target populations and default or scalar parameters 
 
-Accordingly the first script is only for demonstrative purposes and will result in an 
-error when executed with NEST 2.12.
-
 ## Create random connections
 
 NEST random connection rules like `fixed_total_number`, `fixed_indegree` etc. cannot be