Build widevine tests with BOARD_VNDK_VERSION set

The tests are using vendor only libs such as libcdm and libwvlevel3,
thus marked as LOCAL_PROPRIETARY_MODULE to use the libs. In addition,
the dependency to libmedia is changed to libmedia_omx since libmedia is
not available to vendor modules. UniquePtr is replaced with
std::unique_ptr since UniquePtr.h in /libnativehelper is not available
to vendors (and will not be completely removed in a near future).

Bug: 37342627
Test: BOARD_VNDK_VERSION=current m -j tests

Change-Id: I4e9d3267b20c1d52f57664b89f15330e2ebd953d

libwvdrmengine/test/unit/legacy_src/WVDrmFactory_test.cpp

@@ -3,7 +3,6 @@
  */
 
 #include "gtest/gtest.h"
-#include <UniquePtr.h>
 #include "WVDrmFactory.h"
 
 using namespace wvdrm;