Remove 'vsnprintf return value check' item from TODO after code review

The few places where the vsnprintf callers are not checking the return
value, are about to ohshit anyway so there's no real damage by not
doing the check, the rest are harmless.

TODO

@@ -35,8 +35,6 @@ TODO
    - Cleanup status chars -> strings hardcoded mappings all over the place.
      (Fix tied field enum with its dselect description (pkgdisplay.cc))
    - Refactor src/processarc.c.
-   - Make sure all vsnprintf callers are checking the return value, as the
-     system version will not ohsite on us.
    - Fix naming consistency of next/prev members.
    - Split dpkg.h into independent headers.
    - Do more unused header include removal.