Avoid deprecations in examples

Author: aeisenberg

codeql-custom-queries-java/example.ql

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

codeql-custom-queries-javascript/example.ql

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