Avoid recalculating entire permission set after every portal removal in a batch.

When reloading Multiverse-Portals (as is triggered by Multiverse-Adventure), the server hangs for a bit while permissions are recalculated. The time is dependent on the number of Permissibles, Permissions, and Portals. In my case, the server would lock up for 1:30. Looking at the code, I managed to get it down to roughly half that.

In MVPortal.java, I removed lines 170-173. recalculatePermissionDefaults calculates recursively, so the were already recalculated on line 169.

In PortalManager, rather than recalculating the permission set after removing each portal in a batch, I remove them all, delaying the recalculation until they are all removed.

If I missed anything, or need to correct anything, please let me know.

Many thanks,
Joshua Rogers