CXX-1330 Remove RHEL 5.5 Evergreen builder
CXX-1330 Remove RHEL 5.5 Evergreen builder

The C driver no longer tests against this platform, so we shouldn't,
either.

xdg/mongo-cxx-driver,acmorrow/mongo-cxx-driver,mongodb/mongo-cxx-driver,acmorrow/mongo-cxx-driver,mongodb/mongo-cxx-driver,mongodb/mongo-cxx-driver,xdg/mongo-cxx-driver,acmorrow/mongo-cxx-driver,xdg/mongo-cxx-driver,acmorrow/mongo-cxx-driver,mongodb/mongo-cxx-driver,xdg/mongo-cxx-driver