Also forget specialisations and unfoldings because they would need
substitution to be correct. (They get pinned back on separately.)
+Hoever, we REMEMBER loop-breaker and dead-variable information. The loop-breaker
+information is used (for example) in MkIface to avoid exposing the unfolding of
+a loop breaker.
+
\begin{code}
zapFragileInfo :: IdInfo -> Maybe IdInfo
zapFragileInfo info@(IdInfo {occInfo = occ,