Remove use of default-interrupt
sb-sys:default-interrupt was removed from SBCL in commit 5df305ad: https://github.com/sbcl/sbcl/commit/5df305ad28aada106762da1035b3316ff97d872f#diff-ff477d771119e3391dfefcd0debd29a0d0daa533118e6e6859939c7f68e0fc20R69. Backward compatibility should not be an issue as default-interrupt
was just a contraction for enable-interrupt
.