Breaking: #96149 - EXT:form EmailFinisher always uses FluidEmail
See forge#96149
Description
In recent versions, the 
        Email of EXT:form allowed sending
emails with either 
        Standalone or via 
        Fluid, which
has been introduced in TYPO3 v10. The 
        Standalone option has
therefore now been removed together with the Html. and
Plaintext. templates.
Impact
Since the EXT:form 
        Email is now always using 
        Fluid
for sending emails, the 
        template is not evaluated
anymore. For forms, which still define custom templates with this option,
a fallback kicks in, sending the emails with the default EXT:form
        Fluid templates.
Also the 
        use configuration option, previously used to
allow a smooth migration path is now obsolete and can safely be removed
from any form finisher configuration.
Affected Installations
Installations, which have not yet switched to 
        Fluid, while using
custom email templates, configured with 
        template.
Migration
In case you use custom email templates, replace 
        template
with the 
        template and 
        template options. Also
make sure, you have separate template files for the used formats, e.g.
Contact and Contact.