manipulating the WSDL file so that only the main part is there? e.g. 1
You could just manually remove the elements corresponding to the methods you don't need and see if that's enough. You should be able to remove those elements without touching the rest of the file.
https://stackoverflow.com/questions/402160/working-with-large-wsdl-can-we-trim-it
Trying to preprocess the WSDL: It seems there are not tools
Use .gitignore to reduce the amount (and .gitignore documents what we removed).
As discussed in the email from Andreas, can you reduce the files to the ones really needed from NOVA (PreisAuskunft)