[feature]: Remove ErrSynchronizingChain from returned error whitelist

[TonyGiorgio]

Is your feature request related to a problem? Please describe.
When investigating the extent of out of sync LND nodes with lnsploit, I noticed that LND will return ErrSynchronizingChain which gives a human readable "Synchronizing blockchain" error when another node attempts to open a channel when the LND node is out of sync.

This gives an attacker the knowledge it needs to know whether or not a malicious unilateral closure (revoked commitment tx broadcast) could succeed if it previously had a channel with that node already.

Describe the solution you'd like
Move or remove ErrSynchronizingChain from the list of errors that will be returned on the wire. This happens here and it should probably fall back to the "funding failed due to internal error" default since that's exactly what it is.

Describe alternatives you've considered
You could keep the error but exclude it from lnwire or you could add more logic around the human readable data that is returned from this error to be more generic.

Additional context
Related: #7002