cleanup: Remove migrated files

[charlieyu1996]

Target PR: GoogleCloudPlatform/java-docs-samples#7423

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[snippet-bot]

Here is the summary of changes.

You are about to delete 18 region tags.

• samples/snippets/src/main/java/com/example/texttospeech/ListAllSupportedVoices.java:33, tag tts_list_voices
• samples/snippets/src/main/java/com/example/texttospeech/ListAllSupportedVoicesBeta.java:33, tag tts_list_voices
• samples/snippets/src/main/java/com/example/texttospeech/QuickstartSample.java:19, tag tts_quickstart
• samples/snippets/src/main/java/com/example/texttospeech/QuickstartSampleBeta.java:19, tag tts_quickstart
• samples/snippets/src/main/java/com/example/texttospeech/SsmlAddresses.java:19, tag tts_ssml_address_imports
• samples/snippets/src/main/java/com/example/texttospeech/SsmlAddresses.java:44, tag tts_ssml_address_audio
• samples/snippets/src/main/java/com/example/texttospeech/SsmlAddresses.java:91, tag tts_ssml_address_ssml
• samples/snippets/src/main/java/com/example/texttospeech/SsmlAddresses.java:124, tag tts_ssml_address_test
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeFile.java:40, tag tts_synthesize_text_file
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeFile.java:85, tag tts_synthesize_ssml_file
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeFileBeta.java:45, tag tts_synthesize_text_file
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeFileBeta.java:89, tag tts_synthesize_ssml_file
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeText.java:37, tag tts_synthesize_text
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeText.java:80, tag tts_synthesize_text_audio_profile
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeText.java:127, tag tts_synthesize_ssml
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeTextBeta.java:43, tag tts_synthesize_text
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeTextBeta.java:85, tag tts_synthesize_text_audio_profile_beta
• samples/snippets/src/main/java/com/example/texttospeech/SynthesizeTextBeta.java:131, tag tts_synthesize_ssml

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[generated-files-bot]

Warning: This pull request is touching the following templated files:

• samples/snippets/pom.xml