lib/ignore: Remove unused patterns in cache (#9601)

Tiny cleanup I noticed while trying to fix/test another issue
(https://github.com/syncthing/syncthing/pull/9600). I shortly tried to
figure out what it was used for in the past, but gave up without
results.

lib/ignore/ignore.go

@@ -205,7 +205,7 @@ func (m *Matcher) parseLocked(r io.Reader, file string) error {
 	m.curHash = newHash
 	m.patterns = patterns
 	if m.withCache {
-		m.matches = newCache(patterns)
+		m.matches = newCache()
 	}
 
 	return err