Use *macroexpand-hook* in sbcl-world-lock test.

This deadlocks when executed with cold dispatch caches, e.g. with:
make SELECTOR=sbcl-world-lock-1 LISP=sbcl check

* slime-tests.el (sbcl-world-lock): Use *macroexpand-hook*.
* slime-tests.el (sbcl-world-lock): Fix docstring.