Remove commit references from event release history tables

[magnusbaeck]

Description

Some event release history table entries contain references to the commit where the event version was introduced. This is awkward since you can't possibly include such a reference in the commit where it belongs. Working around that problem by using multiple commits or similar isn't worth the effort since you can just use git log to find this information. Let's remove those references and consistently use "No edition set" (or whatever #326 says we should use).

Motivation

Consistency and avoiding SHA-1 references makes for less work updating the event release history tables.

Exemplification

N/A

Benefits

• No hoop-jumping required to get SHA-1 references in the tables.
• More consistent experience for documentation readers and writers alike.

Possible Drawbacks

One could argue that it's a loss to not get commit references in these tables.