Removed non-existing include dir

Change-Id: I3e00a8471e6d94f596a34bdfdb26a0caba23dd82
diff --git a/libc/Android.mk b/libc/Android.mk
index b94e573..b2ac9af 100644
--- a/libc/Android.mk
+++ b/libc/Android.mk
@@ -445,7 +445,6 @@
 # ========================================================
 libc_common_c_includes := \
     $(LOCAL_PATH)/stdlib  \
-    $(LOCAL_PATH)/string  \
     $(LOCAL_PATH)/stdio   \
     external/safe-iop/include