docs/node/grpc: Remove GetSignerNonce from Envoy

Author: peternose

docs/node/grpc.mdx

@@ -125,7 +125,6 @@ static_resources:
     GetLightBlock|\
     GetNextBlockState|\
     GetParameters|\
-    GetSignerNonce|\
     GetStatus|\
     GetTransactions|\
     GetTransactionsWithResults|\