Revert "Add zio constructor/destructor"

This patch was slightly flawed and allowed for zio->io_logical
to potentially not be reinitialized for a new zio. This could
lead to assertion failures in specific cases when debugging is
enabled (--enable-debug) and I/O errors are encountered. It
may also have caused problems when issues logical I/Os.

Since we want to make sure this workaround can be easily removed
in the future (when we have the real fix). I'm reverting this
change and applying a new version of the patch which includes
the zio->io_logical fix.

This reverts commit 2c6d0b1e07b0265f0661ed7851d3aa8d3e75e7a9.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Issue #602
Issue #604