Small update to tests/tinytest.R

[eddelbuettel]

While working on the hot-fix 1.0.13-1 (which is now on CRAN, yay!!), I noticed that tests/tinytest.R still had two assignments only very early tinytest required, plus a call to packageDescription("Rcpp")$Version which can be more compactly written as packageVersion("Rcpp") (and is supported by R 3.5.0 which our oldest CI use). Nothing major, really.

Checklist

• Code compiles correctly
• R CMD check still passes all tests
• Preferably, new tests were added which fail without the change
• Document the changes by file in ChangeLog