systemctl: drop translation of method names to descriptions in error message

systemctl: drop translation of method names to descriptions in error message

We had yet-another table of descriptive strings to use in error messages.
I started thinking how to synchronize them with the strings in logind, but
ultimately I think it's better to remove those altogether. Those strings
should almost never be used: normally if the call fails, logind will provide
an error message itself, which is probably more detailed than what we can
figure out on the client side. And the most important part that we want to
show here is what exactly we called, in particular RebootWithFlags vs. Reboot,
etc. By using the "descriptive strings" we were obfuscating this. So let's just
simplify our code and print the actual method name, since this is more useful
as an error statement that is googlable and unique.

While at it, let's print the correct method name ;)