lnchannel: allow deleting unfunded incoming channels

[f321x]

We tried to delete incoming channels that didn't get funded after lnutil.CHANNEL_OPENING_TIMEOUT, however an assert prevented this:

  3.63 | E | lnwatcher.LNWatcher.[default_wallet-LNW] | Exception in check_onchain_situation: AssertionError()
Traceback (most recent call last):
  File "/home/user/code/electrum-fork/electrum/util.py", line 1233, in wrapper
    return await func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnwatcher.py", line 117, in check_onchain_situation
    await self.update_channel_state(
    ...<5 lines>...
        keep_watching=keep_watching)
  File "/home/user/code/electrum-fork/electrum/lnwatcher.py", line 135, in update_channel_state
    chan.update_onchain_state(
    ~~~~~~~~~~~~~~~~~~~~~~~~~^
        funding_txid=funding_txid,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<2 lines>...
        closing_height=closing_height,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        keep_watching=keep_watching)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnchannel.py", line 341, in update_onchain_state
    self.update_unfunded_state()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/user/code/electrum-fork/electrum/lnchannel.py", line 382, in update_unfunded_state
    self.lnworker.remove_channel(self.channel_id)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnworker.py", line 3244, in remove_channel
    assert chan.can_be_deleted()
           ~~~~~~~~~~~~~~~~~~~^^
AssertionError

[f321x]

Shouldn't lnutil.CHANNEL_OPENING_TIMEOUT = 24*60*60 be higher, like 2 weeks?

BOLT-2 says:

A non-funding node (fundee):
- SHOULD forget the channel if it does not see the correct funding
transaction after a timeout of 2016 blocks.

EDIT:
seems like the timeout was added afterwards:
lightning/bolts@ba00bf8
Will work on block based timeout.