app_queue: Fix minor xmldoc duplication and vagueness.

The F option in the xmldocs for the Queue application
was erroneously duplicated, causing it to display
twice on the wiki. The two sections are now merged into one.

Additionally, the description for the d option was quite
vague. Some more details are added to provide context
as to what this actually does.

ASTERISK-30486 #close

Change-Id: I6706cea708b5cc781f59f8652c2cb377e55aed7e
(cherry picked from commit bad5bda08cf4595ee80aa3dca418ccff6356c98c)