Avoid deprecations in examples

codeql-custom-queries-java/example.ql

@@ -7,6 +7,6 @@
 
 import java
 
-from Block b
+from BlockStmt b
 where b.getNumStmt() = 0
 select b, "This is an empty block."

codeql-custom-queries-javascript/example.ql

@@ -7,6 +7,6 @@
 
 import javascript
 
-from Block b
+from BlockStmt b
 where b.getNumStmt() = 0
 select b, "This is an empty block."