chattr/lsattr: update obsolete attribute support

chattr/lsattr: update obsolete attribute support

* Remove description of and printing of h, which was never visible to
  clients of the EXT4_IOC_GETFLAGS ioctl, including chattr and lsattr.

* Remove descriptions of X and Z, whose support was removed in
  4a05268cf86f713 (Remove compression support).

* Update a brief description of E, whose meaning was changed in
  22f22ab1d2bc5ae (Reserve the codepoints for the new INCOMPAT
  feature ENCRYPT).

* Add P to symbolic mode format string.

Signed-off-by: Tyson Nottingham <tgnottingham@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>