Remove unused protos in python/google/protobuf/internal/more_messages.proto (#18245)

Closes #18245

COPYBARA_INTEGRATE_REVIEW=#18245 from tempoz:tempoz-remove-unused-messages 5133876
PiperOrigin-RevId: 699003107

Author: tempoz

python/google/protobuf/internal/more_messages.proto

@@ -13,10 +13,6 @@ syntax = "proto2";
 
 package google.protobuf.internal;
 
-import "google/protobuf/duration.proto";
-import "google/protobuf/struct.proto";
-import "google/protobuf/timestamp.proto";
-
 // A message where tag numbers are listed out of order, to allow us to test our
 // canonicalization of serialized output, which should always be in tag order.
 // We also mix in some extensions for extra fun.