ext4: unused variables cleanup in fs/ext4/extents.c

ext4 extents cleanup:

  . remove unused `*ex' from check_eofblocks_fl
  . remove unused `*eh' from ext4_ext_map_blocks


Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>