Removed shared_lib flag when running the model

[AlfredMayhew]

Given recent changes to the location of the shared lib (AtChem/AtChem2#535), the shared_lib flag is no longer needed when calling the model, and raises an error. I have removed this to allow models to run correctly.

[AlfredMayhew]

@rs028 , I will merge this unless I'm forgetting something? All I needed to do was remove the shared_lib flag when executing the model, right? I already specify the model/configuration path during the build step, and the --model flag during model execution.
I've tested it and it seems to work.

[rs028]

Yes, I think so. Keep in mind this is an intermediate step and we want to fully move those files out of configuration, which means shared_lib (or something similar) will be re-introduced (see AtChem/AtChem2#539), but since we may decide to use flags for the build script we can do all in one go (no need to break things more than once!).