remove API wrapper

[pmeier]

Before #509, the API wrapper

ragna/ragna/deploy/_ui/api_wrapper.py

Line 12 in 71acf83

class ApiWrapper(param.Parameterized):

made sense, since it gave as a convenient interface around our own REST API. However, after #509 the API wrapper no longer wraps a REST API, but rather a subset of the engine

ragna/ragna/deploy/_engine.py

Line 18 in 71acf83

class Engine:

Thus, we can cleanup the UI code quite a bit by removing the API wrapper completely and just use the engine directly.