Fix the tzdata update tools.

The recent libcore ZoneInfo changes mean that we can no longer
compile libcore's ZoneInfo against the RI. Luckily, the field in
our data file that we needed ZoneInfo for isn't actually used.
This change removes our dependence on libcore.

I've left the field in to avoid a file format change. We can remove
the field if/when we next have a real need to bump the file format.

Bug: 16168653
Change-Id: Iedad2252c2b49f4d8bb2c7d9078b39b622444ca7
diff --git a/libc/tzcode/localtime.c b/libc/tzcode/localtime.c
index 5e4e962..3bbed90 100644
--- a/libc/tzcode/localtime.c
+++ b/libc/tzcode/localtime.c
@@ -2210,7 +2210,7 @@
     char buf[NAME_LENGTH];
     int32_t start;
     int32_t length;
-    int32_t raw_gmt_offset;
+    int32_t unused; // Was raw GMT offset; always 0 since tzdata2014f (L).
   };
 
   size_t id_count = (ntohl(header.data_offset) - ntohl(header.index_offset)) / sizeof(struct index_entry_t);