Add the `Tx` suffix to both ForEachNodeDirectedChannelTx and
FetchNodeFeatures temporarily so that we free up the original names for
other use. The renamed methods will be removed or unexported in an
upcoming commit. The aim is to have no exported methods on the
ChannelGraph that accept a kvdb.RTx as a parameter.
With the previous commit, the AddNode method was removed and since that
was the only method making use of the ForEachChannel on the
GraphCacheNode interface, we can remove that method. Since the only two
methods left just expose the node's pub key and features, it really is
not required anymore and so the entire thing can be removed along with
the implementation of it.
Find and replace all nolint instances refering to the `lll` linter and
replace with `ll` which is the name of our custom version of the `lll`
linter which can be used to ignore log lines during linting.
The next commit will do the configuration of the custom linter and
disable the default one.
We also now use the graph DB's own optional functions. An instance of
the graph is currently still passed to the channeldb's
`CreateWithBackend` function. This will be removed in a later commit
once the two have been completely disjoint.
