math/R: Update to 4.2.2; remove FLANG option

https://hypatia.math.ethz.ch/pipermail/r-announce/2022/000686.html

Remove the FLANG option since lang/flang was removed from the tree on
2022-09-30. In the future, the option can be re-added to use flang that
is part of devel/llvm13+.

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