Do not output empty non-root packages in tests with txt

Mostly to avoid listing every internal package in
kotlin-stdlib/kotlin-reflect, as in
https://github.com/JetBrains/kotlin/blob/acd5b62148d797ffd24c4811d1d663f0c1ae7885/compiler/testData/diagnostics/testsWithUnsignedTypes/conversions/conversionOfSignedToUnsigned.txt#L144

compiler/testData/diagnostics/tests/scopes/kt1579.txt

@@ -14,6 +14,3 @@ package lib {
         }
     }
 }
-
-package user {
-}

compiler/testData/diagnostics/tests/scopes/kt1642.txt

@@ -1,7 +1,2 @@
 package
 
-package a {
-
-    package a.java {
-    }
-}