Remove vpn from FRAMEWORKS_BASE_SUBDIRS

To eliminate build warning.
Reference commit: 44e27b5c74b5f441973561a4f945cb58e0cc45a4
which removed framework/base/vpn.

Change-Id: I539e4bc2a4008c8b9eed74dd53eec1f55db3abe5
diff --git a/core/pathmap.mk b/core/pathmap.mk
index 78dee49..6c6ff2e 100644
--- a/core/pathmap.mk
+++ b/core/pathmap.mk
@@ -88,7 +88,6 @@
 	    sax \
 	    telephony \
 	    wifi \
-	    vpn \
 	    keystore \
 	    icu4j \
 	    voip \