If Onyx is currently installed, and you get the error when trying to uninstall, run the following on a command prompt with administrative priviliges:
sqllocaldb create ObdisianControl
sqllocaldb share ObsidianControl ObsidianOnyx
and try uninstalling again; if Onyx is not currently installed, and you get the error when trying to install, run the following on a command prompt with administrative privileges:
sqllocaldb unshare .\ObsidianOnyx
and try installing again