Removes erroneous WALBERLA_ASSERT check

P1ToP2SurrogateOperator::apply() was testing for

WALBERLA_ASSERT_NOT_IDENTICAL(std::addressof(src), std::addressof(dst));

However, as src is a P1Function and dst a P2Function this cannot be
the case. Leads to a compiler error in debug mode due to "comparison of
distinct pointer types"
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