htlcswitch/test: move preimage cache to server level

In this commit the preimage cache is instantiated on the mock server
level where it belongs. Previously it was a cache shared across all mock
servers.

htlcswitch/test_utils.go

@@ -971,7 +971,6 @@ type hopNetwork struct {
 	feeEstimator *mockFeeEstimator
 	globalPolicy ForwardingPolicy
 	obfuscator   ErrorEncrypter
-	pCache       *mockPreimageCache
 
 	defaultDelta uint32
 }
@@ -979,8 +978,6 @@ type hopNetwork struct {
 func newHopNetwork() *hopNetwork {
 	defaultDelta := uint32(6)
 
-	pCache := newMockPreimageCache()
-
 	globalPolicy := ForwardingPolicy{
 		MinHTLC:       lnwire.NewMSatFromSatoshis(5),
 		BaseFee:       lnwire.NewMSatFromSatoshis(1),
@@ -997,7 +994,6 @@ func newHopNetwork() *hopNetwork {
 		feeEstimator: feeEstimator,
 		globalPolicy: globalPolicy,
 		obfuscator:   obfuscator,
-		pCache:       pCache,
 		defaultDelta: defaultDelta,
 	}
 }
@@ -1028,7 +1024,7 @@ func (h *hopNetwork) createChannelLink(server, peer *mockServer,
 			FetchLastChannelUpdate: mockGetChanUpdateMessage,
 			Registry:               server.registry,
 			FeeEstimator:           h.feeEstimator,
-			PreimageCache:          h.pCache,
+			PreimageCache:          server.pCache,
 			UpdateContractSignals: func(*contractcourt.ContractSignals) error {
 				return nil
 			},