Remove obsolete Nashorn-based scripting tests

Since the Nashorn JavaScript engine was removed in Java 15, these tests
will never be run on a Java 17+ JDK which is required as of Spring
Framework 6.0.

See gh-27919

spring-context/src/test/resources/org/springframework/scripting/support/Messenger.js

@@ -1 +0,0 @@
-function getMessage() { return "Hello World!" }

spring-context/src/test/resources/org/springframework/scripting/support/jsr223-with-xsd.xml

@@ -1,23 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<beans xmlns="http://www.springframework.org/schema/beans"
-	   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-	   xmlns:lang="http://www.springframework.org/schema/lang"
-	   xsi:schemaLocation="http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans-2.0.xsd
-				http://www.springframework.org/schema/lang https://www.springframework.org/schema/lang/spring-lang-4.2.xsd">
-
-	<lang:std id="messengerWithInterface" script-source="classpath:org/springframework/scripting/support/Messenger.js"
-			  script-interfaces="org.springframework.scripting.Messenger"/>
-
-	<lang:std id="refreshableMessengerWithInterface" refresh-check-delay="5000"
-			  script-source="classpath:org/springframework/scripting/support/Messenger.js"
-			  script-interfaces="org.springframework.scripting.Messenger">
-	</lang:std>
-
-	<lang:std id="inlineMessengerWithInterface" engine="JavaScript"
-			  script-interfaces="org.springframework.scripting.Messenger">
-		<lang:inline-script>
-			function getMessage() { return "Hello World!" }
-		</lang:inline-script>
-	</lang:std>
-
-</beans>