Removing unused code

[vytautas-karpavicius]

What changed?
Removed common/locks/idMutex and its tests.

Why?
Not used anywhere.

How did you test it?

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 01846164-56ac-44d8-88f5-6d95b95998eb

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 67 unchanged lines in 11 files lost coverage.
• Overall coverage decreased (-0.02%) to 57.302%

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Files with Coverage Reduction	New Missed Lines	%
common/task/weightedRoundRobinTaskScheduler.go	1	89.64%
common/types/shared.go	1	41.66%
common/task/fifoTaskScheduler.go	2	87.63%
service/history/task/transfer_active_task_executor.go	2	72.15%
common/persistence/nosql/nosqlplugin/cassandra/workflow.go	3	59.1%
service/matching/taskListManager.go	3	76.37%
common/types/mapper/thrift/shared.go	4	63.15%
service/history/task/fetcher.go	4	91.24%
service/history/task/transfer_standby_task_executor.go	4	85.98%
common/persistence/nosql/nosqlplugin/cassandra/workflowParsingUtils.go	14	79.16%

Totals
Change from base Build 01845b92-dbad-46b5-bd33-228a5c801612:	-0.02%
Covered Lines:	85114
Relevant Lines:	148537

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💛 - Coveralls