rename GarbageCollectAsync method

corerepo package name provides sufficient context (even if renamed by
caller)

core/commands/repo.go

@@ -43,7 +43,7 @@ order to reclaim hard disk space.
 			return
 		}
 
-		gcOutChan, err := corerepo.GarbageCollectBlockstore(n, req.Context().Context)
+		gcOutChan, err := corerepo.GarbageCollectAsync(n, req.Context().Context)
 		if err != nil {
 			res.SetError(err, cmds.ErrNormal)
 			return

core/corerepo/gc.go

@@ -14,7 +14,7 @@ type KeyRemoved struct {
 	Key u.Key
 }
 
-func GarbageCollectBlockstore(n *core.IpfsNode, ctx context.Context) (<-chan *KeyRemoved, error) {
+func GarbageCollectAsync(n *core.IpfsNode, ctx context.Context) (<-chan *KeyRemoved, error) {
 
 	keychan, err := n.Blockstore.AllKeysChan(ctx)
 	if err != nil {