election_scheduler::flush() has a race condition

[dsiganos]

It was proven during a debugging session a few months ago that the election scheduler flush was broken and could return prematurely.
It was decided to stop using it and remove the flush functionality.

[dsiganos]

Some more information on this:

election_scheduler::flush is expected to do more than it should.

Test code expects to do the following:

• queue a block in the election scheduler
• call scheduler flush
• expect to find a live election in the AEC for that block

That approach has problems:

• it expects election scheduler to know the internal implementation of AEC and give guarantees about when elections inside the AEC become are started
• it can return even if it did not flush the election scheduler (because it returns when AEC is full)

The election flush is used by wallet, rpm block_confirm command and test code.
The test code can be made to use ASSERT_TIMELY and wait for the election to be started rather than facing it to start.
The roc and wallet dependencies need to be reviewed and make a plan as to how to handle them.