Move the installation of /usr/tests/lib/Kyuafile from src/tests/lib/
to src/lib/. This is to keep the src/tests/ hierarchy unaware of the
rest of the tree, which makes things clearer in general. In particular:
1) Everything related to the construction of /usr/tests/lib/ is kept
in src/lib/. There is no need to think about different directories
and how they relate to each other. (The same applies for libexec,
usr.bin, etc. but these are not yet handled.)
2) src/tests becomes the place to keep cross-functional test programs
and nothing else, which also helps in simplifying things.
Reviewed by: freebsd-testing
Approved by: rpaulo (mentor)
cc21b86f50