src/Composer/Installer/InstallationManager.php
public function uninstall(RepositoryInterface $repo, UninstallOperation $operation)
    {
        $package = $operation->getPackage();
        $installer = $this->getInstaller($package->getType());
        $installer->uninstall($repo, $package);
    }
public function uninstall(RepositoryInterface $repo, UninstallOperation $operation)
    {
        $package = $operation->getPackage();
        $installer = $this->getInstaller($package->getType());
        $installer->uninstall($repo, $package);
    }
Uninstalls package.

@param RepositoryInterface $repo      repository in which to check
@param UninstallOperation  $operation operation instance