Renaming the tag for Medalist

BUR #17078 has been rejected.

rename medalist_(manga) -> medalist

With the upcoming anime adaptation of this manga series, having (manga) on the tag make it seems deprecated and I suggest for something more general like medalist, especially since the tag itself is an unused tag.

Being a single bare English noun, it needs some sort of qualifier to differentiate, from generic tournament medalists and the like.

The bulk update request #17078 (forum #242503) has been rejected by @nonamethanks.