clean up warnings related to transient

[johnynek]

We use transient in many classes to deal with cascading related serialization issues.

We are using it on a number of parameters, which in 2.11 are now warning that is a no-op.

We should verify it is a no-op (make non-serializable args, and see that they still serialize), and remove the transient annotations that are warning.

Example:

[warn] /Users/oscar/oss/scalding/scalding-commons/src/main/scala/com/twitter/scalding/commons/source/VersionedKeyValSource.scala:57: no valid targets for annotation on value codec - it is discarded unused. You may specify targets with meta-annotations, e.g. @(transient @param)
[warn]     implicit @transient codec: Injection[(K, V), (Array[Byte], Array[Byte])]) extends Source