Remove flaky Go DataMGR tests that terminate before read.

[lostluck]

• The two flaky tests both followed the pattern of "remove the instruction prior to a bundle reading it". And tried to assert a specific amount of elements would be read.
• This isn't generally useful behavior.
• There was no guarantee that the element channel would have ingested any data before the removal, short of a read being attempted.
• Their case is better covered in other tests anyway, with deterministic results (eg PartialReadThenEndInstruction, which should always return 0s).

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[jrmccluskey]

LGTM