Remove unused functions from TaskAckManager

[vytautas-karpavicius]

What changed?
Removed few functions and related tests from TaskAckManager.

Why?
Not used.

How did you test it?
Existing tests.

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 01818616-b903-445e-855e-6281468a2fc6

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 70 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.01%) to 57.982%

---

Files with Coverage Reduction	New Missed Lines	%
common/task/weightedRoundRobinTaskScheduler.go	1	89.64%
common/membership/hashring.go	2	83.54%
common/persistence/executionManager.go	2	78.2%
common/persistence/statsComputer.go	2	96.43%
service/matching/taskListManager.go	2	73.77%
common/persistence/nosql/nosqlplugin/cassandra/workflow.go	3	57.59%
common/persistence/sql/sqlExecutionStore.go	5	64.38%
common/task/fifoTaskScheduler.go	5	84.54%
common/persistence/nosql/nosqlplugin/cassandra/workflowUtils.go	8	77.95%
service/history/shard/context.go	9	65.9%

Totals
Change from base Build 018172c3-c0f4-4224-bc77-07a7f98d519f:	-0.01%
Covered Lines:	83942
Relevant Lines:	144772

---

💛 - Coveralls

[mindaugasbarcauskas]

Looks good.