Remove the special case where comparing a dereferenceable_or_null
pointer with null results in captures(none) instead of
captures(address_is_null).
This special case is not entirely correct. Let's say we have an
allocated object of size 2 at address 1 and have a pointer `%p` pointing
either to address 1 or 2. Then passing `gep p, -1` to a
`dereferenceable_or_null(1)` function is well-defined, and allows us to
distinguish between the two possible pointers, capturing information
about the address.
Now that we ignore address captures in alias analysis, I think we're
ready to drop this special case. Additionally, if there are regressions
in other places, the fact that this is inferred as address_is_null
should allow us to easily address them if necessary.
d69ee885cc