Rename property for enabling the snapshot repository

[DavideD]

From enableSonatypeOpenSourceSnapshotsRep to enableCentralSonatypeSnapshotsRep (in gradle.properties).

It was changed in commit c254ebb#diff-49a96e7eea8a94af862798a45174e6ac43eb4f8b4bd40759b5da63ba31ec3ef7R59 as part of the move to Maven Central (#2305).