When removing a vertex group from a Grease Pencil object, if the vertex group is not the last one that was added, the information for the remaining groups weights gets mixed up.

This can be seen as follows:

1. In a new file add a new Grease pencil object.
2. Create a stroke.
3. Add two vertex groups: Group and Group.001
4. Assign all the stroke's points to the first vertex group "Group"
5. Assign some of the stroke's points to the second vertex group "Group.001"
6. Remove the first vertex group "Group"
7. Attempt to select the points of the second vertex group: the information is lost.
8. Add a new vertex group: the vertices that belonged to Group.001 are now assigned to this new vertex group.

It turns out the information pertaining the vertex groups indices is not being updated correctly in the MDeformWeight struct.