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Brogan didn't tell you to delete it, he said wrap it in xen:comment tags. I suggest you revert the template to get the code back again and then follow his instructions. You've then got it there again for future reference in case you need it.
If you're still seeing the sidebar on the forums list page, it'll be because you are using a XenPorta customised layout for this. You will need to remove it first. The 'normal' sidebar will then be displayed and once you apply Brogan's code, the sidebar should disappear.
ACP > XenPorta > Options
In Globalised layouts, untick Index (this will remove the XenPorta layout for the forums list page)
You now need to remove the sidebar from the Portal page
Go to XenPorta > Layouts
Click on the Portal layout and remove all of the sidebar blocks
This will remove the sidebar from the portal page
If there is still a sidebar showing on the portal page, then you have edited the portal layout from the front page using the customise portal link. Click on this and reset the layout. After that, remove the Customise Portal permission from everyone as doing it both from the ACP and the portal page can muck things up.