local-metadata: fix leak in string cleanup
local-metadata: fix leak in string cleanup

g_regex_replace_literal() returns a newly allocated string which is not
freed. Return this string instead of allocating a new one.

MikePetullo/grilo-plugins,GNOME/grilo-plugins,MathieuDuponchelle/grilo-plugins,jasuarez/grilo-plugins,MikePetullo/grilo-plugins,jasuarez/grilo-plugins,grilofw/grilo-plugins,MathieuDuponchelle/grilo-plugins,GNOME/grilo-plugins,MathieuDuponchelle/grilo-plugins,MathieuDuponchelle/grilo-plugins,grilofw/grilo-plugins,MikePetullo/grilo-plugins