Avoid unused param warning in unused definition

[som-snytt]

Avoid warning if method is marked unused.

https://github.com/scala/scala/blob/v2.13.14/src/compiler/scala/tools/nsc/backend/jvm/BCodeSkelBuilder.scala#L99

Avoid warning if parameter type is singleton.

https://github.com/scala/scala/blob/v2.13.14/src/compiler/scala/tools/nsc/ast/TreeDSL.scala#L132

Problem

Probably all unused warnings should be silenced by unused enclosing definition, much like deprecation.