dropPrimaryIndex(true) does not work for def_primary on travel-sample

When setting up a test, I wanted to ensure the primary index was not there first, then add an index. I called .dropPrimaryIndex(true) on the BucketManager, but the "def_primary" still existed. Dropping it by name worked.

Is this because the primary index in this case had a name other than #primary?

In either case, it was a bit confusing. The SDK-RFC doesn't seem to indicate anything special about the .dropPrimaryIndex() method.