Print with newline for ui_print.

Currently the ui_print command between the recovery and updater doesn't
append newline. Updater has to send an extra "ui_print" command without
any argument to get the line break. This looks unnecessary. And not all
the callers (including the ones in bootable/recovery) are following this
protocol when sending the ui_print command.

This CL simplifies the protocol to always print with a newline for
ui_print command. When updating from an old recovery with the new
updater, all the ui_print'd strings would appear in one line as a side
effect. But a) it would only affect the text-mode UI, which won't be
shown to users; b) log files won't be affected.

Bug: 32305035
Test: Apply an update with the new updater on top of an old and new
      recovery image respectively.
Change-Id: I305a0ffc6f180daf60919cf99d24d1495d68749b
diff --git a/install.cpp b/install.cpp
index d3ab213..959a742 100644
--- a/install.cpp
+++ b/install.cpp
@@ -420,11 +420,7 @@
         LOG(ERROR) << "invalid \"set_progress\" parameters: " << line;
       }
     } else if (command == "ui_print") {
-      if (!args.empty()) {
-        ui->PrintOnScreenOnly("%s", args.c_str());
-      } else {
-        ui->PrintOnScreenOnly("\n");
-      }
+      ui->PrintOnScreenOnly("%s\n", args.c_str());
       fflush(stdout);
     } else if (command == "wipe_cache") {
       *wipe_cache = true;