Revert "fix: enable new versions of providers to run on old tfstate f…

…iles Telmate#70…" (Telmate#946)

This reverts commit 60d1a3b.

proxmox/resource_vm_qemu.go

@@ -3167,12 +3167,6 @@ func schema_DiskBackup() *schema.Schema {
 		Type:     schema.TypeBool,
 		Optional: true,
 		Default:  true,
-		// Convert previous integer values of 0/1 to booleans
-		StateFunc: func(val interface{}) string {
-			if val.(string) == "0" {return "false"}
-			if val.(string) == "1" {return "true"}
-			return val.(string)
-		},
 	}
 }