Erase partition without recreating one?
To remove all entries from the GPT and MBR tables, open the Disk Utility application and do the following.


Select your disk. 
Select Partition tab.
Set Partition Layout to "1 Partition". 
Set Format to "Free Space".
Click on the Option... button and select "Master Boot Record".
Click Ok to close the pop up window.
Click the Apply button.


The image below was made just before clicking the Apply button.