Remove the `post_handle_chan_restoration` macro

Remove the `post_handle_chan_restoration` macro

Now that `handle_channel_resumption` can't fail, the error handling
in `post_handle_chan_restoration` is now dead code. Removing it
makes `post_handle_chan_restoration` only a single block, so here
we simply remove the macro and inline the single block into the two
places the macro was used.