multi: replace FundingLocked and funding_locked strings

This commit is created by running the following commands,
```shell
find . -name "*.go" -exec sed -i '' 's/\"FundingLocked/\"ChannelReady/g' {} \;
find . -name "*.go" -exec sed -i '' 's/FundingLocked\"/ChannelReady\"/g' {} \;
find . -name "*.go" -exec sed -i '' 's/\ funding_locked/\ channel_ready/g' {} \;
```

channeldb/channel.go

@@ -1345,7 +1345,7 @@ func (c *OpenChannel) MarkBorked() error {
 }
 
 // SecondCommitmentPoint returns the second per-commitment-point for use in the
-// funding_locked message.
+// channel_ready message.
 func (c *OpenChannel) SecondCommitmentPoint() (*btcec.PublicKey, error) {
 	c.RLock()
 	defer c.RUnlock()