Remove CODEGEN_VERSION from Makefile.prow

[kaovilai]

velero/Makefile.prow

Line 14 in 8c8a6cc

CODEGEN_VERSION := 0.22.2

Seems to not be referenced any more.

[kaovilai]

Removed c07b43a#diff-d7a67317231fdcc9ff848f4a98efba4e15db17f9503e556b598a40e0166c3cb3L77 by @mpryc

[openshift-bot]

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/lifecycle stale

[kaovilai]

/lifecycle frozen