Make agent_name required parameter

Co-authored-by: Muhammad Atif Ali <me@matifali.dev>

filebrowser/main.tf

@@ -20,7 +20,6 @@ data "coder_workspace_owner" "me" {}
 
 variable "agent_name" {
   type = string
-  default = "main"
   description = "The name of the main deployment. (Used to build the subpath for coder_app.)"
 }