Pass permitted_path to the linker as is.

Now that we have the fixed list of whitelisted libraries
there is no longer need to check if java_permitted_path is nullptr.
In fact checking it prevents custom classloaders created by apps
from loading libraries using absolute path.

Bug: http://b/28659864
Change-Id: I1bfc16a573b090f70f078ecccd0e4016939a5dc0
(cherry picked from commit b31caa95ec)

libnativeloader/native_loader.cpp

@@ -101,9 +101,7 @@ class LibraryNamespaces {
                                   nullptr,
                                   library_path.c_str(),
                                   namespace_type,
-                                  !permitted_path.empty() ?
-                                      permitted_path.c_str() :
-                                      nullptr);
+                                  permitted_path.c_str());
 
     if (ns != nullptr) {
       namespaces_.push_back(std::make_pair(env->NewWeakGlobalRef(class_loader), ns));