Import of compiletime.testing nullifies unused lint

[Cherry-picked b325681]

Author: som-snytt

compiler/src/dotty/tools/dotc/transform/CheckUnused.scala

@@ -473,7 +473,6 @@ object CheckUnused:
         if inliners == 0
           && languageImport(imp.expr).isEmpty
           && !imp.isGeneratedByEnum
-          && !imp.isCompiletimeTesting
           && !ctx.owner.name.isReplWrapperName
         then
           if imp.isCompiletimeTesting then