fix: remove unused proto InputText, InputAudio (#500)

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PiperOrigin-RevId: 367294563
Source-Link: googleapis/googleapis@05958a4

Shipping as minor because this is another cleanup after cl/363762006

proto-google-cloud-dialogflow-v2beta1/clirr-ignored-differences.xml

@@ -46,7 +46,11 @@
   </difference>
   <difference>
     <differenceType>8001</differenceType>
-    <className>com/google/cloud/dialogflow/v2beta1/InputTextConfig*</className>
+    <className>com/google/cloud/dialogflow/v2beta1/InputText*</className>
+  </difference>
+  <difference>
+    <differenceType>8001</differenceType>
+    <className>com/google/cloud/dialogflow/v2beta1/InputAudio*</className>
   </difference>
   <difference>
     <differenceType>8001</differenceType>