lnrpc: fix log.go files

The `log.go` file of each subserver is a copy and paste of the others.
All of them have the same typo, an extra space in a comment, and the
the definition of a function not used anywhere.

lnrpc/watchtowerrpc/log.go

@@ -29,19 +29,3 @@ func DisableLog() {
 func UseLogger(logger btclog.Logger) {
 	log = logger
 }
-
-// logClosure is used to provide a closure over expensive logging operations so
-// don't have to be performed when the logging level doesn't warrant it.
-type logClosure func() string // nolint:unused
-
-// String invokes the underlying function and returns the result.
-func (c logClosure) String() string {
-	return c()
-}
-
-// newLogClosure returns a new closure over a function that returns a string
-// which itself provides a Stringer interface so that it can be used with the
-// logging system.
-func newLogClosure(c func() string) logClosure { // nolint:unused
-	return logClosure(c)
-}