Whether or not you create files in Photoshop for online use, every Adobe Photoshop CS5 document contains one slice that covers its file extents. Unless you activate Photoshop's "Slice Select" tool, you'll never see this auto slice. If you've created slices of your own in a file and no longer want them incorporated in it, it's easy to get rid of them and return your file to its original state. If you're seeing a slice that covers your entire document after you've chosen the "Slice Select" tool, getting rid of that slice is easier still.
Switch to the "Slice Select" tool in your Adobe Photoshop CS5 toolbox. Click on each slice you want to delete.
Press the "Delete" or "Backspace" key. Your slices disappear. Photoshop creates auto slices to fill in the area your user slices occupied.
Delete all your user slices to create an auto slice that covers your entire document. You can hide this slice if you do not need to view it.
Choose the "Slice Select" tool from your Adobe Photoshop CS5 toolbox. Click on the "Hide Auto Slices" button in the "Options Bar" on your screen. The single auto slice disappears.
Deselect "Slices" from the "Show" flyout of the "View" menu to make the default auto slice disappear without switching to the "Slice Select" tool. The "Show" flyout offers you control over whether Photoshop displays or hides other "Extras" as well.
Repeat either of these steps if you reactivate auto-slice display accidentally and wish to hide this file feature again. Remember that the single default auto slice does not affect your file or its behaviour.
Remember that creating slices doesn't actually slice your document. Exporting a sliced file and the HTML necessary to display it requires additional steps.