[Tagging] [RFC] Deprecate maxspeed:seasonal:winter

[Marc_marc]

https://wiki.openstreetmap.org/wiki/Proposal:Deprecate_maxspeed:seasonal:winter

Deprecate maxspeed:seasonal:winter only is nonsense,
it's the whole maxspeed:seasonal:* that need to be grouped in one shoot

but we also have maxspeed:wet maxspeed:snow (and maybe other)
it make sens if we want to keep those easy shortcut or not
or convert all of those into more complex (but in only one key) 
maxpseedconditional