SMT2 back-end: CVC5 does not support lambda expressions

I wrongly asserted (in 8fdb8bb) that CVC5 supports lambda. It
seemingly does not, as can also be confirmed using Z3's test
https://github.com/Z3Prover/z3test/blob/master/regressions/smt2/memset.smt2.

Author: tautschnig

src/solvers/smt2/smt2_conv.cpp

@@ -119,7 +119,6 @@ smt2_convt::smt2_convt(
     use_array_of_bool = true;
     use_as_const = true;
     use_check_sat_assuming = true;
-    use_lambda_for_array = true;
     use_datatypes = true;
     break;