Certain Windows services, such as SharePoint Services, install SQL Server Embedded Edition by default as their database. This is the new name for the Windows Internal Database. Unfortunately they don't always uninstall it afterwards.

To remove the 32-bit (x86) version:
msiexec /x {CEB5780F-1A70-44A9-850F-DE6C4F6AA8FB} callerid=ocsetup.exe

To remove the 64-bit (x64) version:
msiexec /x {BDD79957-5801-4A2D-B09E-852E7FA64D01} callerid=ocsetup.exe

Though not required, a reboot after the uninstall is recommended.

References:
Microsoft: Windows Internal Database is not listed in the Add or Remove Programs tool and is not removed when you remove Windows SharePoint Services 3.0 from the computer