Fix some events that won't ever appear, or would appear too often.

Generally speaking, random events should appear in the random event list, exactly once. Not zero times, and not two or more times. There are a few exceptions (like events that are only instantiated as queued events), but exactly once is a good rule of thumb.

• Fixes RE Shelter Inspection, RES Sale, and a whole load of REFS events, which could never appear.
• Makes JE Slave Dispute Slave Deal appear with the correct frequency.
• Sorts the REFS list mostly alphabetically so I can actually find things.

Fixes #3357 (closed)