A heavily patched libical was originally included as part of the kdepim source code. For the Trinity project this was split into an external dependency, as other programs also use libical and there was no more need for the KDE-specific patches to the upstream code. This is a dependency that will need to be filled even for basic functionality.
libcaldav and libcarddav are for the new CalDAV and CardDAV resources, for korganizer and kaddressbook respectively. You can disable them, but you will lose interoperability with newer PIM suites such as Google Calendar and Zimbra.
So libical is required and is a replacement for libkcal?
What about libcaldav? libcarddav? Are there configure options to disable the latter two?
I checked configure --help and saw nothing obvious for all three. :(
I don't see the links for the libcaldav and libcarddav sources. I saw links to deb packages.
Note: Just about everything I select at your quickbuild site uses an "invalid certificate." I hate this so-called feature of Firefox. I know how to add exceptions, but would be nice if folks did not have to do that. :)