build: make curl required by secrets
    
    Also remove --disable-libcurl since it doesn't make sense.
    
    Reviewed-by: Lukáš Slebodník <lslebodn@redhat.com>
    Reviewed-by: Simo Sorce <simo@redhat.com>
    Reviewed-by: Jakub Hrozek <jhrozek@redhat.com>