Remove unused utility methods checking for Java 8 (#8152)

Co-authored-by: Mark Waite <mark.earl.waite@gmail.com>

Author: Chrimle

core/src/main/java/jenkins/util/java/JavaUtils.java

@@ -40,24 +40,6 @@ private JavaUtils() {
         // Cannot construct
     }
 
-    /**
-     * Check whether the current JVM is running with Java 8 or below
-     * @return {@code true} if it is Java 8 or older version
-     */
-    public static boolean isRunningWithJava8OrBelow() {
-        String javaVersion = getCurrentRuntimeJavaVersion();
-        return javaVersion.startsWith("1.");
-    }
-
-    /**
-     * Check whether the current JVM is running with Java 9 or above.
-     * @return {@code true} if it is Java 9 or above
-     */
-    public static boolean isRunningWithPostJava8() {
-        String javaVersion = getCurrentRuntimeJavaVersion();
-        return !javaVersion.startsWith("1.");
-    }
-
     /**
      * Returns the JVM's current version as a {@link VersionNumber} instance.
      */