fix(libs): restore ElvUI-namespaced Ace3 stack clobbered by sweep

The coa-ace3 sweep (commits 0c130e0..5ea6e44, before coa-elvui was added to
EXCLUDED_FORKS in coa-ace3 tools/sweep.py) overwrote ElvUI's customized,
-ElvUI-namespaced Ace3 libs with plain canonical ones. ElvUI registers libs
as AceLocale-3.0-ElvUI and the AceConfig-3.0-ElvUI family (plus -ElvUI
widgets that don't exist in canonical), so the clobber left them
unregistered: ElvUI failed to init (16 locale 'L' errors) and /ec would not
open. Restores ElvUI/Libraries/Ace3/AceLocale-3.0 and the
ElvUI_OptionsUI/Libraries/Ace3 stack to their pre-sweep state (5021fd1).
coa-elvui is now in EXCLUDED_FORKS, so this won't be re-clobbered.

ElvUI_OptionsUI/Libraries/Ace3/AceGUI-3.0/widgets/AceGUIContainer-DropDownGroup.lua

@@ -2,7 +2,7 @@
 DropdownGroup Container
 Container controlled by a dropdown on the top.
 -------------------------------------------------------------------------------]]
-local Type, Version = "DropdownGroup", 22
+local Type, Version = "DropdownGroup", 21
 local AceGUI = LibStub and LibStub("AceGUI-3.0", true)
 if not AceGUI or (AceGUI:GetWidgetVersion(Type) or 0) >= Version then return end
 
@@ -125,7 +125,7 @@ local function Constructor()
 	dropdown.frame:Show()
 	dropdown:SetLabel("")
 
-	local border = CreateFrame("Frame", nil, frame, "BackdropTemplate")
+	local border = CreateFrame("Frame", nil, frame)
 	border:SetPoint("TOPLEFT", 0, -26)
 	border:SetPoint("BOTTOMRIGHT", 0, 3)
 	border:SetBackdrop(PaneBackdrop)