rpc: remove grace period when shutting down the server
rpc: remove grace period when shutting down the server

The server delayed closing of connections for 3s when stopping. This was
supposed to allow for slow handlers, but it didn't really work. When
geth quits, it will just exit immediately after quitting the server.

Removing the timer makes testing easier because all connections will be
closed after Stop returns.

maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum,maran/go-ethereum