OKay... took a while to get home this evening.
So, as promised, the file you're looking for is [
Interface > AddOns > nUI > Layouts > Default > UnitPanels > {panel mode} > nUI_UnitSkin_{panel mode}TgtButton.lua ] -- locate the section copied below and comment out or delete the line I highlighted.
Code:
options =
{
enabled = true,
height = 35,
width = 72,
inset = 3,
strata = nil,
level = nil,
text = nUI_L["Target"],
show_reaction = true,
class_colors = true,
clickable = true,