At tag "edk2-stable201905", the build flags HTTP_BOOT_ENABLE and
TLS_ENABLE have become useless. Their roles have been taken by
NETWORK_HTTP_BOOT_ENABLE and NETWORK_TLS_ENABLE, respectively. Remove the
old build flags.

Cc: Philippe Mathieu-Daud <philmd@redhat.com>
Ref: https://bugs.launchpad.net/qemu/+bug/1831477


Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Philippe Mathieu-Daud <philmd@redhat.com>
Tested-by: Philippe Mathieu-Daud <philmd@redhat.com>