This is a relatively simple tutorial.
Most people do this by deleting a line of code, but what we will be doing is commenting it out. I do it this way so if for whatever reason I want to enable it in the future, I can do so without having to do too much work.
The steps are as follows:
Go into your Admin Control Panel
Click the "Look & Feel" button.
Click the name of the skin you are currently using on your board.
In the left hand side, click on the category "Board Index", then click on "boardIndexTemplate".
Find this code:
<a href='#' id='toggle_sidebar' title='{$this->lang->words['toggle_sidebar']}' data-closed="{$this->lang->words['_laquo']}" data-open="×"> </a>
And replace it with this code:
<!--<a href='#' id='toggle_sidebar' title='{$this->lang->words['toggle_sidebar']}' data-closed="{$this->lang->words['_laquo']}" data-open="×"> </a>-->
That's it! Go and check your sidebars to make sure, though. It may be a good idea to recache your skins, but I didn't find it necessary.
If you are wondering what that did, essentially all we did was commented the code out so the browser ignores it. If for whatever reason you wish to undo what we did, just remove the <!-- and --> at the beginning and end of the modified code. If you think you will forget this, there is always that handy dandy bookmark feature
Hope this helps out some people!