kaboutdata: Move license-related KAboutData enums to KAboutLicense.

In addition to the above, removes a deprecated ctor (and supporting
autotests), and code which was deprecated since KDE4.
I have added an apidox porting note mentioning K4AboutData (the
preferred compatibility route) to compensate.

Another change from the reviewed patch was to correct comments in the
apidox and mention K4AboutData in the class apidox.

ack'ed by ervin. See RR for full description. All tests pass here.

REVIEW:117919