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/duplicateClass/differentGenericArguments.txt

@@ -39,6 +39,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/differentGenericArgumentsReversed.txt

@@ -39,6 +39,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateClass.txt

@@ -40,6 +40,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateNestedClasses.txt

@@ -149,6 +149,3 @@ package p {
 package
 
 public fun test(/*0*/ m1: p.M1): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/duplicateSuperClass.txt

@@ -44,6 +44,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericArgumentNumberMismatch.txt

@@ -39,6 +39,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/genericSuperClass.txt

@@ -70,6 +70,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/members.txt

@@ -48,6 +48,3 @@ package p {
 package
 
 public fun test(/*0*/ a: p.A): kotlin.Unit
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/sameClassNameDifferentPackages.txt

@@ -31,6 +31,3 @@ public final class A {
     public open override /*1*/ /*fake_override*/ fun hashCode(): kotlin.Int
     public open override /*1*/ /*fake_override*/ fun toString(): kotlin.String
 }
-
-package p {
-}

compiler/testData/diagnostics/tests/multimodule/duplicateClass/sameGenericArguments.txt

@@ -39,6 +39,3 @@ package p {
 package
 
 public fun test(): kotlin.Unit
-
-package p {
-}