remove an DCHECK. it is not needed. although the binary operations th…

…at it is guarding are suppoed to work only on more than 1 operand, they can and they are, de facto, used to process expressions with only one operand.

src/common/expression/LogicalExpression.cpp

@@ -10,7 +10,6 @@
 namespace nebula {
 
 const Value &LogicalExpression::eval(ExpressionContext &ctx) {
-  DCHECK_GE(operands_.size(), 2UL);
   switch (kind()) {
     case Kind::kLogicalAnd:
       return evalAnd(ctx);