Remove FOP change bar caveat
Remove FOP change bar caveat

(Changebar support is still not enabled in the FOP-specific toolkit code, but the bundled FOP version supports them in principle, so we'll drop the caveat here and enable support with a future maintenance release.)

- https://github.com/dita-ot/dita-ot/issues/3406
- https://github.com/dita-ot/dita-ot/issues/3407

Signed-off-by: Roger Sheen <a61a1add71dadc74037ae5e44ee30713db9a7451@infotexture.net>

infotexture/docs,dita-ot/docs,infotexture/docs