OutputWriters: remove unused classes and old parser in EclipseWriter

the classes "SimulatorOutput", "SimulatorOutputBase", "OutputWriter"
and "OutputWriterBase" were completely unused in opm-core,
opm-autodiff and opm-parser and where in the way of the old parser
removal. Thus, it is IMHO much better to get rid of them and introduce
abstractions for writing to multiple output formats if there is an
actual need to do so. (so far, these classes were quite specific to
EclipseWriter and were thus just an additional abstraction layer
without any benefit).

the main reason to remove these classes was to get rid of the
old-parser taking methods of EclipseWriter which is also done in this
patch. this avoids quite a few consistency issues and also reduced the
amount of duplicate work required. (if you want these two items
separated, ping me.)