Remove `setPGTStorageDb()` and `setPGTStorageFile()` from the public API.

[adamfranco]

This is just a reminder of things we might want to do for a 2.0 release that already will have breaking changes in the API.

setPGTStorage() should be sufficient for configuring PGT storage systems. Removing setPGTStorageDb() and setPGTStorageFile() will reduce the number of ways to accomplish the same result, lowering the number of code-paths to test.

setPGTStorageDb() and setPGTStorageFile() could be added to a backward-compatibility layer with a deprecation notice.