multi: Removed deprecated interfacer linter

Removed the deprecated interfacer linter from being called for linting.

Also removed the `nolint:interfacer` within the code.

https://github.com/lightningnetwork/lnd/issues/5741

lntest/harness_net.go

@@ -1351,7 +1351,6 @@ func (n *NetworkHarness) WaitForChannelClose(
 // an optional set of check functions which can be used to make further
 // assertions using channel's values. These functions are responsible for
 // failing the test themselves if they do not pass.
-// nolint: interfacer
 func (n *NetworkHarness) AssertChannelExists(node *HarnessNode,
 	chanPoint *wire.OutPoint, checks ...func(*lnrpc.Channel)) error {
 

lntest/itest/assertions.go

@@ -589,9 +589,8 @@ func shutdownAndAssert(net *lntest.NetworkHarness, t *harnessTest,
 
 // assertChannelBalanceResp makes a ChannelBalance request and checks the
 // returned response matches the expected.
-func assertChannelBalanceResp(t *harnessTest,
-	node *lntest.HarnessNode,
-	expected *lnrpc.ChannelBalanceResponse) { // nolint:interfacer
+func assertChannelBalanceResp(t *harnessTest, node *lntest.HarnessNode,
+	expected *lnrpc.ChannelBalanceResponse) {
 
 	resp := getChannelBalance(t, node)
 	require.True(t.t, proto.Equal(expected, resp), "balance is incorrect")