Remove deprecated vad_events and should_interrupt from DeepgramSTTService

Deepgram's built-in VAD events were deprecated in 0.0.99 in favor of
Silero VAD. This removes vad_events from settings and LiveOptions,
the should_interrupt parameter, the vad_enabled property,
_on_speech_started/_on_utterance_end handlers, and simplifies
_on_message and process_frame accordingly.

tests/test_settings.py

@@ -334,7 +334,6 @@ class TestDeepgramSTTSettingsApplyUpdate:
             smart_format=False,
             punctuate=True,
             profanity_filter=True,
-            vad_events=False,
         )
         defaults.update(kwargs)
         return DeepgramSTTSettings(**defaults)
@@ -430,7 +429,6 @@ class TestDeepgramSTTSettingsFromMapping:
             interim_results=True,
             punctuate=True,
             profanity_filter=True,
-            vad_events=False,
         )
 
         raw = {"punctuate": False, "diarize": True}