Removes unnecessary exhaustivestruct linter

I don't see a good reason to keep this. Omitting struct fields to
default to their empty value is how Go works. I don't see much reason to
set slice fields to `nil`, ints to `0`, etc.

The linter itself is archived and has a note in the read me that:

> This linter is meant to be used only for special cases. It is not
> recommended to use it for all files in a project.

Our cases aren't special.

Author: ornj

.golangci.yml

@@ -11,7 +11,6 @@ linters:
     - gomnd
     - godox
     - nlreturn
-    - exhaustivestruct
     - wrapcheck
     - thelper
     - testpackage