Blender Git Loki

Fix T93169: Weightpaint falloff popover drawn twice

This came with {rBf8a0e102cf5e}.

The panel was meant specifically for the gradient tool, but since it was
given the ".weighpaint" context, it would also draw as part of generic
header toolsettings drawing.

Now remove this context on purpose and only draw this specifically from
the gradient tools ToolDef.

Maniphest Tasks: T93169

Differential Revision: https://developer.blender.org/D13268