No warning when attempting to add a non-Additive animation to aim offset

REGRESSION: Yes, working in //UE4/Main at CL 3196079

When attempting to add an animation sequence with the incorrect additive type to a aim offset graph, the user isn't given a warning that this can't be done.

There used to be a warning, but it appears to have been removed in the latest version of the aimoffset graph.

1. Open ContentExamples in editor.
2. Create a new Aim Offset based on Owen_Skeleton and open in.
3. From the Asset Browser, attempt to drag Run_Fwd into the aim offset graph.

RESULT:

The animation isn't added but the user isn't told why.

EXPECTED:

Warning when attempting to add an animation with the wrong additive type to the graph.