Eliminate dependency on doctrine/common

[jwage]

This will require doctrine/dbal 2.8 without common and the work to continue to split up doctrine/common in to separate projects has to be finished.

[stof]

AFAIK, the only part of Doctrine Common used directly in doctrine/migrations is the event part. So as soon as that part is extracted to a dedicated package, we can change the requirement here

[jwage]

It will remove doctrine/common from doctrine/migrations directly, but it will still be pulled in by doctrine/dbal dependency until we upgrade to doctrine/dbal 2.8.

[stof]

But until we use the event system directly, we cannot remove the direct dependency.

[goetas]

Do you thing that #883 addresses this issue?

[alcaeus]

This library already doesn't depend on doctrine/common anymore, so I'm closing this issue. DBAL is tracked separately.