Stripping default nil values for nullable blocks

[lvsti]

With the Xcode 10 toolchain (maybe previously as well but I just found out now), functions that take a nullable block parameter will appear with a nil default value in the generated interface, even if the declaration was part of a protocol. This is weird as in Swift protocol methods cannot define a default value. Moreover, Sourcery/SourceKit fails to properly parse these interfaces and produces garbage type information.

So FYI, I'm planning to manually strip these = nil sequences from the generated interface but I'll make it possible to opt out with a command line flag.