Remove unused variable

src/compiler/checker.ts

@@ -14185,7 +14185,6 @@ namespace ts {
             let hasDuplicateDefaultClause = false;
 
             const expressionType = checkExpression(node.expression);
-            const expressionTypeIsStringLike = maybeTypeOfKind(expressionType, TypeFlags.StringLike);
             forEach(node.caseBlock.clauses, clause => {
                 // Grammar check for duplicate default clauses, skip if we already report duplicate default clause
                 if (clause.kind === SyntaxKind.DefaultClause && !hasDuplicateDefaultClause) {