Remove check that gerrit reporter has params

Since reporters must be specified now (after we added the ability
to have multiple reporters), the right way to make a silent pipeline
is to have no reporters, and the right way to have an experimental
pipeline (non-voting but reporting) is to have a reporter with no
parameters.

Change-Id: I5c979f0d2a6aafe5de4d60d8ce245d9bdcd73dae