init: Simplify struct BuiltinArguments

Make the code that creates BuiltinArguments instances easier to read by
using initializer lists instead of constructor calls. Remove the
BuiltinArguments constructors.

Change-Id: I6cf215a81d298cf7e524e22fb75db820e0225c9a
Signed-off-by: Bart Van Assche <bvanassche@google.com>
diff --git a/init/check_builtins.cpp b/init/check_builtins.cpp
index 481fa31..461ed22 100644
--- a/init/check_builtins.cpp
+++ b/init/check_builtins.cpp
@@ -85,7 +85,7 @@
 }
 
 Result<void> check_exec_reboot_on_failure(const BuiltinArguments& args) {
-    BuiltinArguments remaining_args(args.context);
+    BuiltinArguments remaining_args{.context = args.context};
 
     remaining_args.args = std::vector<std::string>(args.begin() + 1, args.end());
     remaining_args.args[0] = args[0];