Winter code cleanup

[hakman]

Some issues still remain, but very few:

> staticcheck -- ./... | grep -v -e "\.pb\.go" -e "proto" 
pkg/controller/controller.go:779:28: this result of append is never used, except maybe in other appends (SA4010)
pkg/etcdclient/client.go:144:2: empty branch (SA9003)
pkg/hostmount/nsenter.go:47:15: ListProcMounts not declared by package mount (compile)
pkg/hostmount/nsenter.go:94:21: MakeMountArgs not declared by package mount (compile)
pkg/hostmount/nsenter.go:112:31: AddSystemdScope not declared by package mount (compile)
pkg/pki/fs_test.go:126:28: actual.CertPool().Subjects has been deprecated since Go 1.18: if s was returned by SystemCertPool, Subjects will not include the system roots.  (SA1019)
pkg/privateapi/peers.go:301:23: grpc.WithInsecure is deprecated: use WithTransportCredentials and insecure.NewCredentials() instead. Will be supported throughout 1.x.  (SA1019)
pkg/privateapi/peers.go:304:22: grpc.WithBackoffMaxDelay is deprecated: use WithConnectParams instead. Will be supported throughout 1.x.  (SA1019)

/cc @olemarkus @justinsb

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[johngmyers]

This change seems less desirable than what was before.

[hakman]

More or less agree, but staticheck was seeing a possible issue with the code. It's not so bad as it is now either.

[hakman]

Any objection to merging this, now that this has been reverted?

[johngmyers]

/lgtm