TriggerMenu: Remove unused topoStartFrom from the ChainProp class
This MR removes the unused topoStartFrom
variable from the ChainProp
dataclass. This was a remnant from the run 2 R21 TriggerMenu
infrastructure, and @tamartin agreed it could be removed.
I'm also updating the comments above all HLT Menus to remove the mention of this property (and remove the R21-style menu entry example as a list of properties, which is now invalid as well).