Remove empty volumeMounts

Signed-off-by: hs536 <sawamura.hiroki@fujitsu.com>
diff --git a/etc/PruneMavenCache.groovy b/etc/PruneMavenCache.groovy
index f190487..b4d4b05 100644
--- a/etc/PruneMavenCache.groovy
+++ b/etc/PruneMavenCache.groovy
@@ -20,7 +20,6 @@
   - name: jnlp
     image: jenkins/jnlp-slave:alpine
     imagePullPolicy: IfNotPresent
-    volumeMounts:
     env:
       - name: JAVA_TOOL_OPTIONS
         value: -Xmx1G