configuration: adjust references to forbidden properties

The recent change that made deprecated properties either forbidden or
obsolete failed to update some references to these now-forbidden
properties.

This patch fixes these.  It also fixes one typo when defining a
forbidden property, tries to rationalise the use of ${} in comments and
literal property values are placed in single quotes.The SRM description
for QoS plugins has been expanded.

As ReviewBoard was misbehaving, review was via GitHub

Target: master
Acked-by: Gerd Behrmann
Request: 2.10
Request: 2.9
Request: 2.8
Request: 2.7
Request: 2.6