SI-6539 moves @compileTimeOnly away from scala-reflect

The move is done to provide forward compatibility with 2.10.0.

The annotation isn't replaced with one of the macro-based solutions
right away (see comments for more information about those), because
we lack necessary tech in 2.10.x.
Merge pull request #2019 from scalamacros/ticket/6539

SI-6539 moves @compileTimeOnly away from scala-reflect