protodoc: improve handling of oneof (#4908)
protodoc: improve handling of oneof (#4908)

Protodoc improvement for #4739. Remove oneof comment when the oneof declaration only has one field.

Risk Level: Low (doc change only)
Testing: local

Signed-off-by: Lizan Zhou <739047aeb4f72dac9d1867914b065926e8c1008d@tetrate.io>

dnoe/envoy,envoyproxy/envoy-wasm,dnoe/envoy,envoyproxy/envoy,lyft/envoy,istio/envoy,istio/envoy,envoyproxy/envoy,eklitzke/envoy,jrajahalme/envoy,istio/envoy,dnoe/envoy,eklitzke/envoy,lizan/envoy,jrajahalme/envoy,lyft/envoy,lyft/envoy,eklitzke/envoy,envoyproxy/envoy,istio/envoy,lizan/envoy,lizan/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,jrajahalme/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy,jrajahalme/envoy,envoyproxy/envoy,dnoe/envoy,lizan/envoy,lyft/envoy,lizan/envoy,envoyproxy/envoy,istio/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,dnoe/envoy,lyft/envoy,eklitzke/envoy,lizan/envoy,jrajahalme/envoy,istio/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,eklitzke/envoy