funding: rename FundingLocked related functions and variables

This commit is created by running the following commands,
```shell
gofmt -d -w -r 'sendFundingLocked -> sendChannelReady' .

gofmt -d -w -r 'handleFundingLockedMtx -> handleChannelReadyMtx' .

gofmt -d -w -r 'handleFundingLockedBarriers -> handleChannelReadyBarriers' .

gofmt -d -w -r 'receivedFundingLocked -> receivedChannelReady' .

gofmt -d -w -r 'handleFundingLocked -> handleChannelReady' .

gofmt -d -w -r 'fundingLockedSent -> channelReadySent' .

gofmt -d -w -r 'checkPeerFundingLockInterval -> checkPeerChannelReadyInterval' .
```

funding/config_integration.go

@@ -7,5 +7,5 @@ import "time"
 func init() {
 	// For itest, we will use a much shorter checking interval here as
 	// local communications are very fast.
-	checkPeerFundingLockInterval = 10 * time.Millisecond
+	checkPeerChannelReadyInterval = 10 * time.Millisecond
 }