[DSE] Generalize store null to calloc allocated memory [NFC-ish]

This change removes a direct check for calloc-like allocation functions, and instead handles the generic case where we're storing a constant to constant initialized memory.  This is mostly to remove the call to isCallocLike, but if someone downstream happens to have an initialized alloc which initializes to e.g. -1, this will also kick in for them.  (I don't know of such an example ftr.)