chore(general): misc cleanups (#3982)

* chore(general): remove unused `Behavior` type
* chore(test): leverage `testutil.ServerParameters` in server test

internal/feature/feature.go

@@ -6,9 +6,6 @@
 	"fmt"
 )
 
-// Behavior specifies how kopia should behave if it encounters a Feature it does not understand.
-type Behavior string
-
 // IfNotUnderstood describes the behavior of Kopia when a required feature is not understood.
 type IfNotUnderstood struct {
 	Warn             bool   `json:"warn"`                       // warn instead of failing