Revert "[DataStore] Add UT for Observer"

Revert submission 26560594-cherrypicker-L21300030002461779:N81800030040573477

Reason for revert: Build breakages in b/329500917. 

Reverted changes: /q/submissionid:26560594-cherrypicker-L21300030002461779:N81800030040573477

Change-Id: I89d6785aaf1bfd4b1bd5a2f92f0594582b80efb0
4 files changed