Remove unused NewFrontendClient functions

[vytautas-karpavicius]

What changed?
Cleanup unused NewFrontendClient and NewFrontendClientWithTimeout functions.

Why?
To remove unused code.
We create our frontend clients via NewFrontendClientWithTimeoutAndConfig - which is used when creating DNS based cluster clients.

How did you test it?

Potential risks

Release notes

Documentation Changes

[coveralls]

Pull Request Test Coverage Report for Build 95278358-57f0-4142-8841-4e0de0a326bb

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 49 unchanged lines in 15 files lost coverage.
• Overall coverage increased (+0.003%) to 56.714%

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Files with Coverage Reduction	New Missed Lines	%
common/types/shared.go	1	26.64%
client/history/client.go	2	40.32%
client/history/metricClient.go	2	45.94%
common/task/weightedRoundRobinTaskScheduler.go	2	89.64%
service/history/execution/mutable_state_builder.go	2	69.77%
service/history/handler.go	2	48.32%
service/history/queue/timer_queue_processor.go	2	59.33%
service/history/shard/context.go	2	65.93%
service/history/task/transfer_active_task_executor.go	2	70.93%
service/matching/matcher.go	2	91.46%

Totals
Change from base Build b1ed06a4-e64b-45c3-a7a9-4eab3790ab47:	0.003%
Covered Lines:	81040
Relevant Lines:	142893

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💛 - Coveralls