Remove reverse indentation from zed comments.

Remove all occurrences of reverse indentation from zed comments for
consistency within the project code base.

Signed-off-by: Chris Dunlap <cdunlap@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2695
Remove obsolete comment about guard pages

Remove an obsolete comment that refers to code removed by commit
79c6e4c4. The code and comment related to space consumed by guard
pages in user-space stacks, which we no longer take into account.

Signed-off-by: Ned Bass <bass6@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2722
Merge branch 'master' of github.com:zfsonlinux/zfs