pkgbase: generate dependencies in generate-ucl.sh

This cuts out a large chunk of duplicated *.ucl files that just needed
dependencies tacked on, and gives generate-ucl.sh some leeway in case a
future pkg may need more than one dependency.

Run-through to determine which ones could simply be removed done with for i
in *.ucl; do diff -U3 template.ucl ${i}; done | less and inspecting for any
differences beyond just adding deps at the end. The remaining ucl files are
basically all differently-licensed, require scripts, or are marked vital.

I've opted to remove %PKGDEPS% entirely without regard for third-party ucl,
as pkgbase is not yet considered production. However, I do not hold a strong
position on this and there is approximately 0 chance it will return.

clibs should have been added previously in generate-ucl.sh as one that
doesn't have any dependencies, but do so now that we would otherwise be
tacking on the runtime dependency.

Reviewed by: manu, bapt (earlier version)
Differential Revision: https://reviews.freebsd.org/D23415