rBa8f7d41d3898 added a "duplicate" check for being in curves sculptmode
unnecessarily afaict (`in_sculpt_curve_mode` in addition to the
previously existing `in_curves_sculpt_mode`).
Over time, the later evolved to also take into account the output of a
viewer node, see rBc55d38f00b8c (the previously existing
`in_curves_sculpt_mode` did not receive this).
This all results in the fact that selection is not drawn with a viewer
node (can be useful though, and there are separate opacity controls for
both selection and the viewer attribute, so these can be used/blended to
everyones liking).
So now deduplicate the check.
Differential Revision: https://developer.blender.org/D16467
ed852c8401