Remove VFS object reference counting

kernel/vfs/vfs.c

@@ -107,13 +107,7 @@ VfsObj *vfs_open(char *mountpoint, const char *path, uint32_t flags) {
 }
 
 void vfs_close(VfsObj *vobj) {
-  if (vobj->refs < 0) {
-    return;
-  }
-  vobj->refs--;
-  if (vobj->refs == 0) {
-    vobj->cleanup(vobj);
-  }
+  vobj->cleanup(vobj);
 }
 
 void vfs_init(void) {

kernel/vfs/vfs.h

@@ -39,7 +39,6 @@ typedef struct VfsStat {
 
 typedef struct VfsObj {
   SpinLock spinlock;
-  int32_t refs;
   void *extra;
   size_t extrasize;
   struct VfsMountPoint *vmp;