Avoided redundant EngineController creation

Found this while investigating memory leaks through CLR Profiler. We are unnecessarily creating ```EngineController``` in the constructor of ```DynamoController```. Remove this line makes the following difference as indicated by CLR Profiler (both these numbers are obtained by just launching Dynamo and closing it down).

##### Before removal

```
Allocated bytes:                162,528,272
Relocated bytes:                 76,849,582
Final Heap bytes:                25,543,222
Objects finalized:                    1,321
Critical objects finalized:           1,172
Gen 0 collections:                       24
Gen 1 collections:                        8
Gen 2 collections:                        3
Induced collections:                      1
Gen 0 Heap bytes:                 6,803,236
Gen 1 Heap bytes:                 7,462,987
Gen 2 Heap bytes:                17,543,690
Large Object Heap bytes:            377,480
Handles created:                     17,174
Handles destroyed:                   14,123
Handles surviving:                    3,051
Heap Dumps:                               0
Comments:                                 0
```

##### After removal

```
Allocated bytes:                140,123,591
Relocated bytes:                 76,864,879
Final Heap bytes:                25,517,276
Objects finalized:                    1,546
Critical objects finalized:           1,367
Gen 0 collections:                       23
Gen 1 collections:                        7
Gen 2 collections:                        3
Induced collections:                      1
Gen 0 Heap bytes:                 6,115,452
Gen 1 Heap bytes:                 5,307,437
Gen 2 Heap bytes:                14,197,600
Large Object Heap bytes:            636,968
Handles created:                     17,148
Handles destroyed:                   14,097
Handles surviving:                    3,051
Heap Dumps:                               0
Comments:                                 0
```