make ApkIndexDependency conform to ApkIndexRequirementRef

dunno if this is necessary for the graph to work but we'll see

Sources/apk/Index/ApkIndexProvides.swift

@@ -6,7 +6,7 @@
 struct ApkIndexProvides: ApkIndexRequirementRef {
   let name: String
 
-  init(extract: String) throws(ApkRequirement.ParseError) {
-    (self.name, _) = try ApkRequirement.extract(blob: extract)
+  init(name: String, version _: ApkVersionSpecification) {
+    self.name = name
   }
 }