SI-7070 Revert implementation restriction on companions in pkg objs

The implementation restriction created from SI-5954 has two problems.

1) The problematic code works fine if compile with sbt. That means the
restriction is breaking some people needlessly.

2) It's not binary compatible.

The implementation restriction needs to be reverted.

This commit reverts 3ef487ecb6733bfe3c13d89780ebcfc81f9a5ea0