This removes the assertion that a copy of a moved-from SmallSetIterator
equals the original, which is illegal due to SmallSetIterator including
an instance of a standard std::set iterator.
C++ [iterator.requirements.general] states that comparing singular
iterators has undefined result:
Iterators can also have singular values that are not associated with
any sequence. [...] Results of most expressions are undefined for
singular values; the only exceptions are destroying an iterator that
holds a singular value, the assignment of a non-singular value to an
iterator that holds a singular value, and, for iterators that satisfy
the Cpp17DefaultConstructible requirements, using a value-initialized
iterator as the source of a copy or move operation.
This assertion triggers the following error in the GNU C++ Library in
debug mode under EXPENSIVE_CHECKS:
/usr/include/c++/8.2.1/debug/safe_iterator.h:518:
Error: attempt to compare a singular iterator to a singular iterator.
Objects involved in the operation:
iterator "lhs" @ 0x0x7fff86420670 {
state = singular;
}
iterator "rhs" @ 0x0x7fff86420640 {
state = singular;
}