[css-display] editorial: some "Expands to:" tooltips are wrong

[MatsPalmgren]

https://drafts.csswg.org/css-display/#the-display-properties
When hovering <display-outside> etc, there are duplicates and unwanted text items.
For example, hovering <display-inside> lists all values twice, and also has an illegal "flow layout" value.
The same problem occurs in <display-internal> and other places.

[tabatkins]

Woo, done! That was harder than I expected.

• The illegal "flow layout" value (and a few other illegal values) are a result of bad markup. I've fixed in the ED, but we need to push a fixed WD to avoid other specs getting those values.
• The duplication was an accidental result of some other refactoring work I did. Fixed now.