Revert "Break metadata into smaller chunks (number of chunks=10) for faster delta generation."

This reverts commit 4e8a306bb126b80e1d64a5e799a14e8aa6b55762.

BUG=chromium-os:10669
TEST=Unit tests

Review URL: http://codereview.chromium.org/6014014

Change-Id: Id582cbb6f1289dde119eff9f18ea78d350cd21ab
diff --git a/metadata.cc b/metadata.cc
index 7dfc787..20c0a0d 100644
--- a/metadata.cc
+++ b/metadata.cc
@@ -220,7 +220,7 @@
 
     // Due to bsdiff slowness, we're going to break each block group down
     // into metadata chunks and feed them to bsdiff.
-    __u32 num_chunks = 10;
+    __u32 num_chunks = 4;
     __u32 blocks_per_chunk = num_metadata_blocks / num_chunks;
     __u32 curr_block = bg_start_block;
     for (__u32 chunk = 0; chunk < num_chunks; chunk++) {