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/resolve/implicitReceiverProperty.txt

@@ -20,12 +20,6 @@ package a {
     }
 }
 
-package b {
-}
-
-package c {
-}
-
 package test {
     public val x1: kotlin.Int
     public val x3: kotlin.Int