ignore interfaces for `inheritance-graph` printer

[0xPhaze]

Describe the desired feature

Interfaces can clutter the output of the inheritance graph printer and don't add much value. Perhaps these should be removed by default from the output.

[0xalpharush]

Potentially this can be updated https://github.com/crytic/slither/tree/fix-inheritance-printer

[0xalpharush]

We should make this the default instead of a flag #2153

We should also remove virtual functions which aren't overridden
https://crytic.github.io/slither/slither/core/declarations/function.html#Function.is_virtual