chore: remove migrated samples

[Shabirmean]

• Remove the sample that was migrated in chore: migrated left out samples GoogleCloudPlatform/java-docs-samples#7468
• This PR is related to previous PR: cleanup: remove migrated sample #1067
• During the first phase of the migration some samples were left behind due to not being referenced in the docs
• However, some of them are deemed necessary. So migrating them in chore: migrated left out samples GoogleCloudPlatform/java-docs-samples#7468 and removing it from here.

[snippet-bot]

Here is the summary of changes.

You are about to delete 3 region tags.

• samples/snippets/src/main/java/com/example/dialogflow/ConversationManagement.java:19, tag dialogflow_create_conversation
• samples/snippets/src/main/java/com/example/dialogflow/ConversationProfileManagement.java:19, tag dialogflow_create_conversation_profile_article_suggestion
• samples/snippets/src/main/java/com/example/dialogflow/ParticipantManagement.java:19, tag dialogflow_create_participant

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