Revert "[Topics API] Implement feature flag guarded encryption."

This reverts commit 70884ab1b4ecb9563db68e725b0ea64717b812df.

Reason for revert: TopicsJsonMapperTest#getTopicJson failing b/311487135

Change-Id: Ia9fb8e779c8d92085a614016c1ff13dd28960dce
13 files changed