gnutls: Fix free_function ccode-attribute of Certificate
gnutls: Fix free_function ccode-attribute of Certificate

Remove an extra space which breaks null-safe free-wrapper generation.

Thanks to getzze

https://bugzilla.gnome.org/show_bug.cgi?id=788181

frida/vala,GNOME/vala,frida/vala,frida/vala,GNOME/vala,GNOME/vala,frida/vala,GNOME/vala,frida/vala