SI-8316 SI-8318 SI-8248 reintroduces resetAllAttrs

Unfortunately, due to the aforementioned bugs we have to delay our triumph
over resetAllAttrs.

Therefore, I'm rolling back the internal changes to scalac introduced in
https://github.com/scala/scala/pull/3485. Our public reflection API interface
in Scala 2.11 is still going to contain only resetLocalAttrs, but both
the reifier and the label typechecker are too heavily addicted to resetAllAttrs
to do away with it right now.