trim: Add a more condensed usage message for error cases.

trim: Add a more condensed usage message for error cases.

When explicitly asking for help, ("apitrace help trim" or "apitrace
trim --help"), the complete help message is still provided.

But when an error case triggers a usage message, (such as an invalid
command-line argument), a more compact usage message is provided so as
to not overwhelm the error message (such as "invalid argument:
--foo").