update_engine: Remove the duplicate BlocksInExtents

This patch removes the duplicate BlocksInExtents from extent_utils.h and fixes
the remainder of the code to reflect this change.

BUG=none
TEST=unittests pass;

Change-Id: I76f5106f75072b20cd8f41f081b2f2b07aeac9a8
Reviewed-on: https://chromium-review.googlesource.com/812009
Commit-Ready: Amin Hassani <ahassani@chromium.org>
Tested-by: Amin Hassani <ahassani@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Reviewed-by: Alex Deymo <deymo@google.com>
Reviewed-by: Sen Jiang <senj@chromium.org>
diff --git a/payload_generator/graph_utils.cc b/payload_generator/graph_utils.cc
index 2d5fb63..4829b21 100644
--- a/payload_generator/graph_utils.cc
+++ b/payload_generator/graph_utils.cc
@@ -104,9 +104,9 @@
 template<typename T>
 void DumpExtents(const T& field, int prepend_space_count) {
   string header(prepend_space_count, ' ');
-  for (int i = 0, e = field.size(); i != e; ++i) {
-    LOG(INFO) << header << "(" << GetElement(field, i).start_block() << ", "
-              << GetElement(field, i).num_blocks() << ")";
+  for (const auto& extent : field) {
+    LOG(INFO) << header << "(" << extent.start_block() << ", "
+              << extent.num_blocks() << ")";
   }
 }