smt expr: revert the limit on lambda subst

turns out that having multiple lambdas around is even slower.. :/

smt/expr.cpp

@@ -2075,7 +2075,7 @@ expr expr::load(const expr &idx, uint64_t max_idx) const {
 
   } else if (isConstArray(val)) {
     return val;
-  } else if (isLambda(val) && !hit_half_memory_limit()) {
+  } else if (isLambda(val)) {
     return val.subst_var(idx).foldTopLevel();
   }