Stop logging when path is excluded

This causes logging a lot and reporting to sentry which can
cause performance issues.

(cherry picked from commit 6eb4563f)

internal/staticpages/servefile.go

@@ -37,7 +37,6 @@ func (s *Static) ServeExisting(prefix urlprefix.Prefix, cache CacheMode, notFoun
 		// %20 in their name.
 		relativePath, err := s.validatePath(prefix.Strip(r.URL.Path))
 		if err != nil {
-			log.WithRequest(r).WithError(err).Error()
 			notFoundHandler.ServeHTTP(w, r)
 			return
 		}