CORE-1219. Removed empty DatabaseException catch blocks in LockService

Removed empty DatabaseException catch blocks around database.rollback() calls in the LockService, which were believed to hide the real cause of the problem described in the incident. Initially, it was thought that no databse.rollback() was being called, thus leaving the Oracle lock hanging. However, the code inspection revealed that database.rollback() must have been called (as it was alreay in the finally blocks); however, it must have failed for some reason, and this reason was not reported due to empty DatabaseException catch blocks.