Prune matching replace directives in staging repos more effectively

[liggitt]

What type of PR is this?
/kind cleanup

What this PR does / why we need it:
As more of our dependencies add go.mod files, it exposed a gap in the part of update-vendor.sh that prunes replace directives from staging go.mod files.

As a reminder:

• replace directives pin to a specific version of dependencies
• they are not effective in library modules, only the main module being built gets to declare effective replace directives
• we prune replace directives that match the naturally required version in our staging go.mod files to highlight where we are pinning to different versions than what is preferred, and try to trend the number of replace directives to zero

#77370 exposed a gap in the way we detected the naturally preferred version was the same as our pinned version.

go mod tidy will completely drop require directives for transitive dependencies we don't actually use any packages from. After those require directives are dropped, go list -m -json all will report the version of those transitive dependencies our direct dependencies prefer (even though it doesn't really matter for purposes of the build, since we're not using any packages from that dependency).

Moving the pruning step before go mod tidy allows us to drop unneeded replace directives for these unused transitive dependencies correctly.

Does this PR introduce a user-facing change?:

NONE

/cc @dims @apelisse

[dims]

/approve
/lgtm

good to see that the unnecessary golang.org/x/text replace from code-generator is gone. thanks @liggitt

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This pull-request has been approved by: dims, liggitt

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