The vmdk you see is a snapshot vmdk. This means at some point you created a snapshot of this disk.
The way to merge the snapshot data to the base disk, is to right click on the VM in your inventory and select the "Snapshot Manager", then select the snapshot and click "Delete". Don't worry, this does not actually delete the file right away, it first merges it into its parent and then deletes the file. This can be done online. Depending on the actual size of the snapshot it could take some time to complete.
André