Remove an unused callback

RTIR 1.0 contained a link to "About RTIR" but this callback stopped
existing in 3.8.4, meaning that it hasn't worked for most of RTIR
2.4/2.6 or any of 3.0.

Removed in the PersonalQuickbar refactoring of 02eebfe4 in rt.git and we
didn't keep backcompat for the callback.
Don't require every RTIR page to use a custom header

The callback to change the 3 things we want to change has existed since
at least RT 3.5.1 fb115741.  This paves the way for core RT components
that we want to exist under /RTIR/ to just need a tiny shim rather than
a full copy and paste of the component with a change to the Header line.

We can probably safely remove /RTIR/Elements/Header in a future RTIR
release and simplify even more code.
RTIR now has the standard Forward

For some reason, RTIR only had "forward transaction" despite RT 3.8
shipping with both "forward ticket" and "forward transaction".  This
went unfixed because it was a copy of old code.  Remove the copied code,
add a top level actions Forward and take advantage of just passing
through to the core code.

Fixes issues #23511
Merge branch '3.2/core-forward'