Parece que você acabou de excluir alguns arquivos no Finder.
Supondo que você usou o instalador de aqui , você precisa seguir as instruções no guia sobre a desinstalação:
Uninstallation
If you need to uninstall PostgreSQL, you can run the uninstaller that is created during the installation process at any time. Note that the uninstaller will never remove your data directory, or the service user account. You can find the uninstaller in the installation directory, and can run it as you ran the installer. No command line options are generally required. On Windows, you can also run the uninstaller from the Add/Remove Programs control panel applet.
Em outras palavras, basta executar o desinstalador instalado com o restante do programa.