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/multiplatform/topLevelFun/headerAndImplInDIfferentPackages.txt

@@ -9,9 +9,6 @@ package common {
 // -- Module: <m2-jvm> --
 package
 
-package common {
-}
-
 package jvm {
     public actual fun foo(): kotlin.Unit
 }
@@ -20,9 +17,6 @@ package jvm {
 // -- Module: <m3-js> --
 package
 
-package common {
-}
-
 package js {
     public actual fun foo(): kotlin.Unit
 }