internal/pkg: delete stale done channels

There is no reason to keep these around.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pkg/pkg.go

@@ -293,6 +293,7 @@ func (c *Cache) finaliseIdent(
 	} else {
 		c.ident[*id] = *checksum
 	}
+	delete(c.identPending, *id)
 	c.identMu.Unlock()
 
 	close(done)