Switch "system/core/base" ref to "system/libbase"

BUG: 148941208
Test: TH
Change-Id: Ifa87b06ad7cfce94ed9b5be6b1ee0c358e52aba1
diff --git a/base b/base
deleted file mode 120000
index 622c552..0000000
--- a/base
+++ /dev/null
@@ -1 +0,0 @@
-../libbase
\ No newline at end of file