Updating the arguments passed into mx::loadLibraries to better accomm…

…odate relocating the MaterialX libraries folder.

Specify the libraries folder location with the PXR_MATERIALX_STDLIB_DIR variable.

Fixes #1586

(Internal change: 2183770)

pxr/imaging/hdSt/materialXFilter.cpp

@@ -458,10 +458,9 @@ HdSt_ApplyMaterialXFilter(
     if (mtlxSdrNode) {
 
         // Load Standard Libraries/setup SearchPaths (for mxDoc and mxShaderGen)
-        mx::FilePathVec libraryFolders = { "libraries", };
+        mx::FilePathVec libraryFolders;
         mx::FileSearchPath searchPath;
         searchPath.append(mx::FilePath(PXR_MATERIALX_STDLIB_DIR));
-        searchPath.append(mx::FilePath(PXR_MATERIALX_BASE_DIR));
         mx::DocumentPtr stdLibraries = mx::createDocument();
         mx::loadLibraries(libraryFolders, searchPath, stdLibraries);