issue: #34553
when rootcoord trigger graceful stop progress, it will block until all
rpc finished. for create collection request, rootcoord need to block
until datacoord finish to watch all channels, but datacoord need to call
`rootcoord.Alloc` during watch channel, and rootcoord doesn't respond to
new request anymore. which cause create collection stucks, and graceful
stop progress stucks.
This PR remove the func call `rootcoord.Alloc` to solve the logic dead
lock during graceful stop progress.
Signed-off-by: Wei Liu <wei.liu@zilliz.com>