[FLINK-19923][coordination] Remove unused BulkSlotProvider, its implementation and tests

[azagrebin]

BulkSlotProvider and its implementation (#12375) is not used any more because it was introduced for the removed OneSlotPerExecutionSlotAllocator (#12256) replaced by SlotSharingExecutionSlotAllocator (#13071) for the PipelinedRegionSchedulingStrategy.

The PR removes the dead code.

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[zhuzhurk]

LGTM.

[XComp]

LGTM. The PhysicalSlotProviderImplTest contains to tests testBulkSlotAllocationFulfilledWithAvailableSlots and testBulkSlotAllocationFulfilledWithNewSlots which I stumbled upon just because of them including "bulkslot". But this is completely unrelated, is it?

[azagrebin]

Thanks for the review @zhuzhurk @XComp

@XComp the tests in PhysicalSlotProviderImplTest are indeed unrelated but there is no Bulk in there as well. It is a confusing leftover and I added a hotfix commit to remove it from test names.