remove repeated error message on failure

[imjasonh]

Cobra logs error messages before passing them to us, so we don't need to re-log it.

Before:

ko build ./blah
Error: failed to publish images: importpath "ko://./blah" is not supported: importpath is not `package main`
2023/01/04 11:30:41 error during command execution:failed to publish images: importpath "ko://./blah" is not supported: importpath is not `package main`
exit status 1

After:

go run . build ./blah
Error: failed to publish images: importpath "ko://./blah" is not supported: importpath is not `package main`
exit status 1