[fuchsia] Remove obsolete //zircon/public/lib/... references.

These targets are now aliases to //zircon/system/ulib/... ones
so update the references in this BUILD.gn file to allow removal
of the aliases in the future.

See https://fxbug.dev/70426 for details.

Change-Id: I5357a36a65581bf3a8fb5e8a194aa94770f51935
1 file changed