Consider use simple event serialization without some properties instead of symfony serializer

There is strong performance impact in using symfony serializer:

branch new_simple_event_serialization (completely without symfony serializer):
```
bin/behat --tags="~@wip&&@parallel" --parallel=3 features/
...................................................................... 70
..................

3 scenarios (3 passed)
88 steps (88 passed)
1m3.391s
```

branch use_null_context (only use NullContext instead of createContext()):
```
bin/behat --tags="~@wip&&@parallel" --parallel=3 features/
...................................................................... 70
..................

3 scenarios (3 passed)
88 steps (88 passed)
1m35.58s
```

branch master:
```
bin/behat --tags="~@wip&&@parallel" --parallel=3 features/
...................................................................... 70
..................

3 scenarios (3 passed)
88 steps (88 passed)
2m9.258s
```

In addition to performance improvements we can remove patched behat usage