Deprecate Package.getInternalSubPackage, simplify DepedencyResolver

source/dub/dub.d

@@ -1843,18 +1843,7 @@ private class DependencyVersionResolver : DependencyResolver!(Dependency, Depend
 			if (!basepack) return null;
 			if (auto sp = m_dub.m_packageManager.getSubPackage(basepack, subname, true))
 				return sp;
-			if (!basepack.subPackages.canFind!(p => p.path.length)) {
-				// note: external sub packages are handled further below
-				auto spr = basepack.getInternalSubPackage(subname);
-				if (!spr.isNull) {
-					auto sp = new Package(spr.get, basepack.path, basepack);
-					m_remotePackages[sp.name] = sp;
-					return sp;
-				}
-				logDiagnostic("Sub package %s doesn't exist in %s %s.", name, name.main, dep);
-				return null;
-			}
-			logDiagnostic("External sub package %s %s not found.", name, dep);
+			logDiagnostic("Subpackage %s@%s not found.", name, dep);
 			return null;
 		}
 

source/dub/package_.d

@@ -312,13 +312,7 @@ class Package {
 		writeJsonFile(filename, m_info.toJson());
 	}
 
-	/** Returns the package recipe of a non-path-based sub package.
-
-		For sub packages that are declared within the package recipe of the
-		parent package, this function will return the corresponding recipe. Sub
-		packages declared using a path must be loaded manually (or using the
-		`PackageManager`).
-	*/
+	deprecated("Use `PackageManager.getSubPackage` instead")
 	Nullable!PackageRecipe getInternalSubPackage(string name)
 	{
 		foreach (ref p; m_info.subPackages)

source/dub/packagemanager.d

@@ -515,9 +515,6 @@ class PackageManager {
 
 	/** Gets the a specific sub package.
 
-		In contrast to `Package.getSubPackage`, this function supports path
-		based sub packages.
-
 		Params:
 			base_package = The package from which to get a sub package
 			sub_name = Name of the sub package (not prefixed with the base