Remove deprecated .net core 2.X version lines
Remove deprecated .net core 2.X version lines

Signed-off-by: Andrew Meyer <8896544cf29336d4c9052e18824ce3ac60d2aadc@vmware.com>

cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci,cloudfoundry/buildpacks-ci