Fix build with assimp 5.1
Origin: Arch linux
        (https://github.com/archlinux/svntogit-packages/tree/packages/qt5-quick3d/trunk)

diff --git a/src/plugins/assetimporters/assimp/assimpimporter.cpp b/src/plugins/assetimporters/assimp/assimpimporter.cpp
index f3660fdd..0f5fc901 100644
--- a/src/plugins/assetimporters/assimp/assimpimporter.cpp
+++ b/src/plugins/assetimporters/assimp/assimpimporter.cpp
@@ -1082,9 +1082,7 @@ void AssimpImporter::generateMaterial(aiMaterial *material, QTextStream &output,
         }
 
         // SpecularGlossiness Properties
-        bool hasSpecularGlossiness;
-        result = material->Get(AI_MATKEY_GLTF_PBRSPECULARGLOSSINESS, hasSpecularGlossiness);
-        if (result == aiReturn_SUCCESS && hasSpecularGlossiness) {
+        {
 
             // diffuseFactor (color) // not used (yet), but ends up being diffuseColor
 //            {