Deprecate unused getSubPackagePath

While looking at the subpackage code, I was wondering
why more places didn't call getSubPackagePath instead
of getSubPackageName, and that is because subpackages
can only be one level deep.

source/dub/recipe/packagerecipe.d

@@ -32,11 +32,18 @@ import std.process : environment;
 	example, "packa:packb:packc" references a package named "packc" that is a
 	sub package of "packb", which in turn is a sub package of "packa".
 */
+deprecated("This function is not supported as subpackages cannot be nested")
 string[] getSubPackagePath(string package_name) @safe pure
 {
 	return package_name.split(":");
 }
 
+deprecated @safe unittest
+{
+	assert(getSubPackagePath("packa:packb:packc") == ["packa", "packb", "packc"]);
+	assert(getSubPackagePath("pack") == ["pack"]);
+}
+
 /**
 	Returns the name of the top level package for a given (sub) package name of
 	format `"basePackageName"` or `"basePackageName:subPackageName"`.
@@ -62,8 +69,6 @@ string getSubPackageName(string package_name) @safe pure
 
 @safe unittest
 {
-	assert(getSubPackagePath("packa:packb:packc") == ["packa", "packb", "packc"]);
-	assert(getSubPackagePath("pack") == ["pack"]);
 	assert(getBasePackageName("packa:packb:packc") == "packa");
 	assert(getBasePackageName("pack") == "pack");
 	assert(getSubPackageName("packa:packb:packc") == "packb:packc");