A quick guide on how to remove the bubble background from unity launcher. However there is no official way but there is a workaround available to replace the original files with the edited. Root access is required.
Unsettings GUI lets you to alter the default Unity desktop environment in Ubuntu. It changes the personal settings in Unity but not the hardware or system settings. Unsettings provides you a one place to change all unity settings, from unity launcher, panel to your privacy settings.