update_engine: Remove unused IsIdempotentOperation().

All the minor-version=2 are idempotent, so since we switched to minor
version 2, this function becomes trivial now. This patch removes this
function from the code and moves the ExtentRanges class to the
payload_generator/ directory since now it is only used there.

BUG=None
TEST=Unittest still pass.

Change-Id: Ib9dbbdded0ca2ef2128bb6c470de7a00720c4038
Reviewed-on: https://chromium-review.googlesource.com/275806
Reviewed-by: Alex Deymo <[email protected]>
Tested-by: Alex Deymo <[email protected]>
Commit-Queue: Alex Deymo <[email protected]>
diff --git a/payload_generator/extent_utils_unittest.cc b/payload_generator/extent_utils_unittest.cc
index 6e685e0..b9f9ef2 100644
--- a/payload_generator/extent_utils_unittest.cc
+++ b/payload_generator/extent_utils_unittest.cc
@@ -9,8 +9,8 @@
 
 #include <gtest/gtest.h>
 
-#include "update_engine/extent_ranges.h"
 #include "update_engine/payload_constants.h"
+#include "update_engine/payload_generator/extent_ranges.h"
 #include "update_engine/test_utils.h"
 
 using std::vector;