OptionalObsoleteFiles: remove GCC remnants

g++ and cc1plus were GCC components that are already removed
unconditionally in ObsoleteFiles.inc.

Reported by: jhb (in review D33108)
Fixes: 57f804675e65 ("remove GCC 4.2.1 build infrastructure")
Sponsored by: The FreeBSD Foundation

(cherry picked from commit 1b9344add475179e4ee6b13f25def6f44799a929)