package: Remove docc plugin dependency

Author: simonjbeaumont

Package.swift

@@ -43,7 +43,6 @@ let package = Package(
     dependencies: [
         .package(url: "https://github.com/apple/swift-openapi-runtime", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-http-types", from: "1.0.0"),
-        .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
         .package(url: "https://github.com/apple/swift-collections", from: "1.0.0"),
     ],
     targets: [