travis: replace recently missing links for libyaml

Rerunning previously passing integration test shows that the
multilibbed libyaml libraries are no longer available from
/usr/lib alongside other libs - maybe an OS upgrade, or an
upstream packaging error?
* .travis.yml (install): Remove libyaml-dev reinstall.
Run a shell find command to link the multilib libyaml libs
back into /usr/lib.  If this command starts failing in future
then it should mean libyaml has moved back to the proper place
and we're failing to relink it manually, so this workaround
can be removed.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>