Some cleanup & 2.10 deprecation upheaval

Enacts the 2.10 drop.
Removes deprecations w.r.t. Scala 2.11.
Removes unused members, imports.
non-trivial parts commented on below.

Oh, yes, of course. And the [implementation](https://github.com/scala/scala/blob/2.12.x/src/reflect/scala/reflect/internal/StdNames.scala#L422) forwards through to `getterName`. What was I thinking ?