If you need to manually remove CoreMelt plugins for some reason, this is the locations where files are installed. In most cases you will never need to do a manual uninstall, please see our instructions on using our uninstaller tool.
/Library/Application Support/Final Cut Pro/Templates.localized/Effects.localized/*PRODUCT NAME*
/Library/Application Support/Final Cut Pro/Templates.localized/Generators.localized/*PRODUCT NAME*
/Library/Application Support/Final Cut Pro/Templates.localized/Titles.localized/*PRODUCT NAME*
/Library/Application Support/Final Cut Pro/Templates.localized/Transitions.localized/*PRODUCT NAME*
Please note the four directories above are in the /Library folder on the top level of your system drive, not the library folder inside your user directory. The CoreMelt *PRODUCT NAME* starts with C2 in each case so you can easily tell which ones are the CoreMelt plugins if you have many plugins installed from other sources.
Removing the above will stop the plugins appearing inside you host application. You may also which to remove additional support files located in these directories.