Moved out public proto IDLs to cadence-idls repository

[vytautas-karpavicius]

What changed?
This is sibling PR for cadence-workflow/cadence-idl#64 - public proto IDLs were moved to cadence-idls repository.
Here we remove public proto files, update idls submodule and create a symlink from previous public folder to point to idls submodule.

Why?
To reuse proto IDLs within Cadence clients.

How did you test it?
Regenerated proto files

rm .build/protoc
make .build/protoc
make fmt

Potential risks
Proto generation may be broken.

Release notes

Documentation Changes

[vytautas-karpavicius]

-L to follow symlinks

[coveralls]

Pull Request Test Coverage Report for Build 63162965-d851-49f8-a8a4-843892914d04

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 57 unchanged lines in 12 files lost coverage.
• Overall coverage decreased (-0.03%) to 59.702%

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Files with Coverage Reduction	New Missed Lines	%
client/history/client.go	2	44.78%
client/history/metricClient.go	2	49.43%
common/task/fifoTaskScheduler.go	2	84.54%
service/history/execution/mutable_state_builder.go	2	69.85%
service/history/handler.go	2	46.59%
service/history/queue/transfer_queue_processor.go	2	57.37%
service/history/task/transfer_standby_task_executor.go	2	90.77%
service/matching/taskListManager.go	2	74.72%
service/frontend/workflowHandler.go	4	56.72%
service/history/execution/context.go	6	65.64%

Totals
Change from base Build 45e2b378-e3a5-4aac-aa26-589b3ee57b09:	-0.03%
Covered Lines:	87655
Relevant Lines:	146822

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💛 - Coveralls