Remove default mode from Ffa functions

Fortnite doesn't really have a permanently set mode, because they changed all the time 

e.g. at the time of this PR competitions is in Duos, but by 2025 they are using Trios (as non team) instead (and could changed again in future)

components/match2/wikis/fortnite/match_group_input_custom.lua

@@ -22,9 +22,7 @@ local MatchFunctions = {
 	},
 	DEFAULT_MODE = 'team'
 }
-local FfaMatchFunctions = {
-	DEFAULT_MODE = 'solos',
-}
+local FfaMatchFunctions = {}
 local MapFunctions = {}
 local FfaMapFunctions = {}