account_preferences should not show the setting for signatures if there is no permission for signatures

[ge66]

Affected version

XF2

This is an old one saw it again when fixing xf2.3 templates.

If all "Signature permissions" are set to NO, the "Show people's signatures with their messages" should not be shown.

This code in account_preferences should only be used if people can set up a signature:

<xf:option name="option[content_show_signature]" checked="{$xf.visitor.Option.content_show_signature}"
                    label="{{ phrase('show_peoples_signatures_with_their_messages') }}" />