inline-r: move `R_LIBS` tests into main testsuite

[ConnorBaker]

The tests introduced in https://github.com/tweag/HaskellR/pull/394 can likely be moved into the main test suite. Instead of producing a test binary for each, consider using process to set the environment variable as part of each test.

[facundominguez]

If they depend on H, perhaps they will need to be migrated to the H package.