Stop converting relative symlinks to absolute.

There's no reason to make them absolute, simply store in the metadata
the target file as is. This vastly simplifies the code and makes all
test pass correctly.

bin/xbps-pkgdb/check_pkg_symlinks.c

@@ -77,7 +77,7 @@ check_pkg_symlinks(struct xbps_handle *xhp, const char *pkgname, void *arg)
 			continue;
 		}
 		snprintf(path, sizeof(path), "%s/%s", xhp->rootdir, file);
-		if ((lnk = xbps_symlink_target(xhp, path, tgt)) == NULL) {
+		if ((lnk = xbps_symlink_target(path)) == NULL) {
 			xbps_error_printf("%s: broken symlink %s (target: %s)\n", pkgname, file, tgt);
 			broken = true;
 			continue;