sys/gnu/vfs/ext2fs: Remove|avoid duplicated macro definitions

sys/gnu/vfs/ext2fs: Remove|avoid duplicated macro definitions

- There are EXT2_ROOTINO and EXT2_ROOT_INO, but using EXT2_ROOTINO
  is probably appropriate on dfly (and it does use EXT2_ROOTINO)
  considering it's been used by userspace, and other fs have it in
  NAME_ROOTINO format.

- WINO is from UFS, but ext2 has it for bad inode for ondisk inode.

- NDADDR and NIADDR (# of slots for direct/indirect block) should be
  defined using existing ext2 ondisk definitions.
  (or maybe don't even use NDADDR and NIADDR, but these two should be
  kept as dfly ext2 code is UFS based and UFS heavily uses these two)

- Remove MAXSYMLINKLEN since there is EXT2_MAXSYMLINKLEN and only
  EXT2_MAXSYMLINKLEN is being used. It also conflicts with UFS version
  of MAXSYMLINKLEN in vfs/ufs/dinode.h.

- (Note that dfly's ext2 seems to be broken currently)