Remove the mechanism to comment out "attribute"

Source/Atomic/Graphics/Shader.cpp

@@ -102,9 +102,6 @@ bool Shader::BeginLoad(Deserializer& source)
 #ifdef ATOMIC_OPENGL
     vsSourceCode_.Replace("void VS(", "void main(");
     psSourceCode_.Replace("void PS(", "void main(");
-    // ATOMIC BEGIN - reported shader compiler error here: https://github.com/urho3d/Urho3D/issues/870
-    psSourceCode_.Replace("attribute ", "// attribute ");
-    // ATOMIC END
 #endif
 
     RefreshMemoryUse();