Remove ComputeSourceHash mode in FileSystemVerification action.

This mode was used to calculate the source partition hash before download
the payload, and we will verify it against the hash in the payload.
Now that we are using per-operation source hash, this mode is no longer
needed.

Test: ./update_engine_unittests
Test: cros_workon_make update_engine --test
Bug: 26972259

Change-Id: Ie30a38cfd9f94e4efe02dfc8664e6785018261f6
diff --git a/update_attempter.cc b/update_attempter.cc
index 81f2ab0..751eb52 100644
--- a/update_attempter.cc
+++ b/update_attempter.cc
@@ -610,9 +610,6 @@
                              false));
   shared_ptr<OmahaResponseHandlerAction> response_handler_action(
       new OmahaResponseHandlerAction(system_state_));
-  shared_ptr<FilesystemVerifierAction> src_filesystem_verifier_action(
-      new FilesystemVerifierAction(system_state_->boot_control(),
-                                   VerifierMode::kComputeSourceHash));
 
   shared_ptr<OmahaRequestAction> download_started_action(
       new OmahaRequestAction(system_state_,
@@ -640,9 +637,8 @@
               new LibcurlHttpFetcher(GetProxyResolver(),
                                      system_state_->hardware())),
           false));
-  shared_ptr<FilesystemVerifierAction> dst_filesystem_verifier_action(
-      new FilesystemVerifierAction(system_state_->boot_control(),
-                                   VerifierMode::kVerifyTargetHash));
+  shared_ptr<FilesystemVerifierAction> filesystem_verifier_action(
+      new FilesystemVerifierAction(system_state_->boot_control()));
   shared_ptr<OmahaRequestAction> update_complete_action(
       new OmahaRequestAction(
           system_state_,
@@ -658,25 +654,20 @@
 
   actions_.push_back(shared_ptr<AbstractAction>(update_check_action));
   actions_.push_back(shared_ptr<AbstractAction>(response_handler_action));
-  actions_.push_back(shared_ptr<AbstractAction>(
-      src_filesystem_verifier_action));
   actions_.push_back(shared_ptr<AbstractAction>(download_started_action));
   actions_.push_back(shared_ptr<AbstractAction>(download_action));
   actions_.push_back(shared_ptr<AbstractAction>(download_finished_action));
-  actions_.push_back(shared_ptr<AbstractAction>(
-      dst_filesystem_verifier_action));
+  actions_.push_back(shared_ptr<AbstractAction>(filesystem_verifier_action));
 
   // Bond them together. We have to use the leaf-types when calling
   // BondActions().
   BondActions(update_check_action.get(),
               response_handler_action.get());
   BondActions(response_handler_action.get(),
-              src_filesystem_verifier_action.get());
-  BondActions(src_filesystem_verifier_action.get(),
               download_action.get());
   BondActions(download_action.get(),
-              dst_filesystem_verifier_action.get());
-  BuildPostInstallActions(dst_filesystem_verifier_action.get());
+              filesystem_verifier_action.get());
+  BuildPostInstallActions(filesystem_verifier_action.get());
 
   actions_.push_back(shared_ptr<AbstractAction>(update_complete_action));