Fix SharedFunctions.AssertionModule.exp_is_constraint

[sim642]

LAnd, LOr and LNot are constraint regardless of what's in their arguments (they don't need a != 0 added outside if something is non-constraint inside).

This caused us to not validate some witnesses containing trivial invariants in #1897 (comment).
For example x >= 0 && 1 does not need to be turned into (x >= 0 && 1) != 0 because one argument of && contains a non-constraint. Such doubly-constraint expression is not supported by our Apron conversion.
Instead, it can stay as it is, so the x >= 0 part is supported, but just the 1 part will be unsupported (#1610), which is irrelevant.

[sim642]

I did verify-validate sv-benchmarks runs on level02.

There's an increase in the number of confirmed invariants:

There are now 50 more self-validated witnesses: https://goblint.cs.ut.ee/results/307-all-validate-level02-pr-1904-after/table-generator-cmp.table.html#/table?filter=1(0*status*(status(notIn(true)),category(notIn()))),3(0*status*(status(in(true)),category(notIn()))).
These mostly overlap with #1897 (comment), because it's a different way to deal with the same issue: instead of not generating trivial invariants, don't be bothered about triviality during validation. But we should have both PRs regardless because this also helps with validation of other tools' witnesses because there are others who also have generated trivial invariants.