zodb/storage: Delegate zurl opts extract to drivers

We can't extract storage client options in general-purpose zodburi
opener, because zodburi aren't standardized. Each storage may define its
own syntax, therefore it is better if this is done decentralized and
independent in each local storage driver.

go/zodb/storage.go

@@ -106,10 +106,6 @@ func OpenDriver(ctx context.Context, zurl string, opt *DriverOptions) (_ IStorag
 		return nil, InvalidTid, err
 	}
 
-	// XXX commonly handle some options from url -> opt?
-	// (e.g. ?readonly=1 -> opt.ReadOnly=true + remove ?readonly=1 from URL)
-	// ----//---- nocache
-
 	opener, ok := driverRegistry[u.Scheme]
 	if !ok {
 		return nil, InvalidTid, fmt.Errorf("zodb: URL scheme \"%s:\" not supported", u.Scheme)