impl(v3): remove deprecated Bigtable admin classes#15920

scotthart merged 6 commits intogoogleapis:prepare-for-v3.0.0googleapis/google-cloud-cpp:prepare-for-v3.0.0from

scotthart:v3_remove_deprecated_bigtable_admin_2scotthart/google-cloud-cpp:v3_remove_deprecated_bigtable_admin_2Copy head branch name to clipboard