Go: add drop instance models (#14485)

### What problem does this PR solve?

1. drop instance model
2. Fix issue of drop instance but not drop models.

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

Signed-off-by: Jin Hai <haijin.chn@gmail.com>

internal/cli/admin_parser.go

@@ -700,8 +700,6 @@ func (p *Parser) parseAdminDropCommand() (*Command, error) {
 		return p.parseDropUser()
 	case TokenRole:
 		return p.parseDropRole()
-	case TokenModel:
-		return p.parseDropModelProvider()
 	case TokenDataset:
 		return p.parseDropDataset()
 	case TokenChat: