remove is_method_error call

An `is_method_error` is not appropriate after an sdbus `call` since
`call` will always throw an exception.  Remove the pointless call
and instead catch the exception.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Iac59331eb31ef7b4c31f21ce4463c6bc7cf83e56
diff --git a/util.cpp b/util.cpp
index 492e954..db104bf 100644
--- a/util.cpp
+++ b/util.cpp
@@ -106,8 +106,11 @@
             auto method = bus.new_method_call(SYSTEMD_BUSNAME, SYSTEMD_PATH,
                                               SYSTEMD_INTERFACE, "KillUnit");
             method.append(JOURNAL_UNIT, "main", signal);
-            bus.call(method);
-            if (method.is_method_error())
+            try
+            {
+                bus.call(method);
+            }
+            catch (sdbusplus::exception_t&)
             {
                 lg2::error("Failed to kill journal service");
                 break;