fix: do not use openai-gpt-4o-mini as the default summary provider (#1984)

lua/avante/providers/init.lua

@@ -273,9 +273,6 @@ end
 
 function M.get_memory_summary_provider()
   local provider_name = Config.memory_summary_provider
-  if provider_name == nil then
-    if M.openai.is_env_set() then provider_name = "openai-gpt-4o-mini" end
-  end
   if provider_name == nil then provider_name = Config.provider end
   return M[provider_name]
 end