[FAB-14324] update named imports in gossip_impl.go
[FAB-14324] update named imports in gossip_impl.go

- remove explicit name for protobuf/proto
- use 'pg' to refer to protos/gossip

Change-Id: I7a441faa9f4e7211dd90891238834f63b5ffffa7
Signed-off-by: Matthew Sykes <89c6e4c9c1046731a9c37abefc223a83de36a5d9@us.ibm.com>

muralisrini/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,stemlending/fabric,binhn/fabric,binhn/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,binhn/fabric,manish-sethi/fabric,hyperledger/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,jimthematrix/fabric,manish-sethi/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,stemlending/fabric,jimthematrix/fabric,muralisrini/fabric,hyperledger/fabric,stemlending/fabric