multi: fix linter issues

This commit fixes outstanding linter issues, that we're not found by
running `make lint` locally. The linter issues were found by running
`docker run -v $(pwd):/build loop-tools golangci-lint run --whole-files`

I added the `revive` to the excludes as it would be to much of a
refactor and IMO seems unneccesary. E.g.
`interface.go:222:6: exported: type name will be used as
loop.LoopInTerms by other packages, and that stutters; consider
 calling this InTerms (revive)`. I think `loop.LoopInTerms` is fine.

test/context.go

@@ -62,7 +62,6 @@ func (ctx *Context) NotifySpend(tx *wire.MsgTx, inputIndex uint32) {
 	}:
 	case <-time.After(Timeout):
 		ctx.T.Fatalf("htlc spend not consumed")
-
 	}
 }
 
@@ -76,7 +75,6 @@ func (ctx *Context) NotifyConf(tx *wire.MsgTx) {
 	}:
 	case <-time.After(Timeout):
 		ctx.T.Fatalf("htlc spend not consumed")
-
 	}
 }
 

test/lnd_services_mock.go

@@ -115,7 +115,7 @@ type RouterPaymentChannelMessage struct {
 	TrackPaymentMessage
 }
 
-// SingleInvoiceSubscription contains the single invoice subscribers
+// SingleInvoiceSubscription contains the single invoice subscribers.
 type SingleInvoiceSubscription struct {
 	Hash   lntypes.Hash
 	Update chan lndclient.InvoiceUpdate