remove useless comment

Author: xuwenhao

20_tts_and_azure.ipynb

@@ -20,7 +20,6 @@
     "import os\n",
     "import azure.cognitiveservices.speech as speechsdk\n",
     "\n",
-    "# This example requires environment variables named \"SPEECH_KEY\" and \"SPEECH_REGION\"\n",
     "speech_config = speechsdk.SpeechConfig(subscription=os.environ.get('AZURE_SPEECH_KEY'), region=os.environ.get('AZURE_SPEECH_REGION'))\n",
     "audio_config = speechsdk.audio.AudioOutputConfig(use_default_speaker=True)\n",
     "\n",