The rules that trigsimp uses (trigrule1, ..., htrigrule1,...) appear in the infolist 'rules'. This means that kill(rules) kills them. That breaks trigsimp. Since trigsimp is a built-in Maxima facility, kill(rules) should not break it.
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Reported by Chris Sangwin in mail in the following way:
trigsimp(0) => 0
kill(allbut [functions])
trigsimp(0) => ERROR trigrule1 not found#0