fmt: Remove unused sliceutil

internal/sliceutil/sliceContains.go

@@ -1,15 +0,0 @@
-package stringslice
-
-func Contains(slice []string, search string) bool {
-	for _, candidate := range slice {
-		if search == candidate {
-			return true
-		}
-	}
-
-	return false
-}
-
-func Append(slice []string, element string) {
-	slice = append(slice, element)
-}