Remove replace directive from go.mod

[perdasilva]

#1471 was failing on the windows go-releaser gha due to:

# github.com/Microsoft/hcsshim/internal/oc
Error: C:\Users\runneradmin\go\pkg\mod\github.com\!microsoft\[email protected]\internal\oc\errors.go:21:39: undefined: errdefs.ToGRPC

This issues is fixed on v0.12.8 (containerd/containerd#10857).

To get the version bump to pass, I've had to add a replace directive to our go.mod

replace github.com/Microsoft/hcsshim => github.com/Microsoft/hcsshim v0.12.8

We need to remove this when containerd gets bumped again and includes the fixed library.

[grokspawn]

Looks like this was done in 16d1fcf