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/signrpc/log.go

@@ -5,7 +5,7 @@ import (
 	"github.com/lightningnetwork/lnd/build"
 )
 
-// log is a logger that is initialized with no output filters.  This
+// log is a logger that is initialized with no output filters. This
 // means the package will not perform any logging by default until the caller
 // requests it.
 var log btclog.Logger
@@ -27,19 +27,3 @@ 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)
-}