mariadb: remove dangling symlink

There was a symlink `libmariadb.a` → `libmariadbclient.a`
but we are removing the latter file. This causes `nixos-rebuild`
to complain:

    system-path> warning: creating dangling symlink

Let’s remove the symlink as well.

pkgs/servers/sql/mariadb/default.nix

@@ -106,7 +106,7 @@ commonOptions = packageSettings: rec { # attributes common to both builds
   postInstall = ''
     # Remove Development components. Need to use libmysqlclient.
     rm "$out"/lib/mysql/plugin/daemon_example.ini
-    rm "$out"/lib/{libmariadbclient.a,libmysqlclient.a,libmysqlclient_r.a,libmysqlservices.a}
+    rm "$out"/lib/{libmariadb.a,libmariadbclient.a,libmysqlclient.a,libmysqlclient_r.a,libmysqlservices.a}
     rm -f "$out"/bin/{mariadb-config,mariadb_config,mysql_config}
     rm -r $out/include
     rm -r $out/lib/pkgconfig