Remove strings deprecated in 3.8

No manual post-integration testing needed, covered by automatic tests.

1. Automated testing passes successfully
2. Review code and make sure there are no usages of deprecated string
3. Confirm removals from each deprecated.txt file match corresponding lang file changes
4. Confirm the following command returns empty:

   $ find . -path "*/en/*" -type f -exec grep -l -i "deprecated.*3\.[78]" "{}" \;