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/multimodule/duplicateMethod/functionGenericsInParamsNotIs.txt

@@ -45,6 +45,3 @@ package
 
 public fun test(/*0*/ b: p.B?): kotlin.Unit
 public fun test1(/*0*/ b: p.B?): kotlin.Unit
-
-package p {
-}