Swing timer: bars fill from duration objects, drop the OnUpdate

Each bar fills itself from a duration object of the swing, a text
binding counts it down, and the marker with its glows rides the fill's
edge. One C_Timer per bar ends the swing, runs the melee grace and
switches a hunter's reload to the deadzone. Colors update on the events
that change them, ACTIONBAR_UPDATE_STATE standing in for the per-tick
IsCurrentAction reconcile; a bar waiting past its grace hides on
STOP_AUTOATTACK or leaving combat. The three bar builders become one.

The Swing Timer throttle setting only paced the OnUpdate, so it goes.

libs/libthrottle.lua

@@ -33,7 +33,6 @@ libthrottle.presetNames = {
 libthrottle.defaults = {
   tooltip_cursor       = "fastest",
   chat_tab             = "custom",
-  swingtimer           = "custom",
 }
 
 -- Convert FPS to throttle delay in seconds
@@ -156,7 +155,6 @@ libthrottle:SetScript("OnEvent", function()
     -- Set defaults for custom fields if missing
     if not _G.pfUI_throttle.tooltip_cursor_custom then _G.pfUI_throttle.tooltip_cursor_custom = "10" end
     if not _G.pfUI_throttle.chat_tab_custom then _G.pfUI_throttle.chat_tab_custom = "10" end
-    if not _G.pfUI_throttle.swingtimer_custom then _G.pfUI_throttle.swingtimer_custom = "50" end
     
     this:UnregisterEvent("PLAYER_ENTERING_WORLD")
   end