multi: replace FundingLocked related docs

This commit replaces `FundingLocked` found in docs using the following
command,
```shell
find . -name "*.go" -exec sed -i '' 's/FundingLocked/ChannelReady/g' {} \;
find . -name "*.go" -exec sed -i '' 's/FundingLock/ChannelReady/g' {} \;
```

htlcswitch/switch_test.go

@@ -82,7 +82,7 @@ func TestSwitchAddDuplicateLink(t *testing.T) {
 // TestSwitchHasActiveLink tests the behavior of HasActiveLink, and asserts that
 // it only returns true if a link's short channel id has confirmed (meaning the
 // channel is no longer pending) and it's EligibleToForward method returns true,
-// i.e. it has received FundingLocked from the remote peer.
+// i.e. it has received ChannelReady from the remote peer.
 func TestSwitchHasActiveLink(t *testing.T) {
 	t.Parallel()