[R] Use either `make sync-cpp` or bootstrap.R not both

[assignUser]

Describe the enhancement requested

After #39147 added a bootstrap.R which does the same as make sync-cpp we have a bit of a redundancy. It would be nice to clean that up.

Maybe we want to automate more of the release steps (as I started in the PR but removed for clarity)

Component(s)

R

[github-actions]

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