Use original opengraph dependency (#17855)

The PR is now merged with the original repo, so we can remove
the temporary replace.

https://focalboard-community.octo.mattermost.com/workspace/zyoahc9uapdn3xdptac6jb69ic?id=285b80a3-257d-41f6-8cf4-ed80ca9d92e5&v=495cdb4d-c13a-4992-8eb9-80cfee2819a4&c=59af323d-35a7-4312-87a1-e374239a03d9

```release-note
NONE
```

go.mod

@@ -144,8 +144,6 @@ require (
 	willnorris.com/go/imageproxy v0.10.0
 )
 
-replace github.com/dyatlov/go-opengraph => github.com/agnivade/go-opengraph v0.0.0-20201221052033-34e69ee2a627
-
 // Hack to prevent the willf/bitset module from being upgraded to 1.2.0.
 // They changed the module path from github.com/willf/bitset to
 // github.com/bits-and-blooms/bitset and a couple of dependent repos are yet